Perch Forms creates a blank sub-page to the page the form was on

I have created a form as part of a multi-item region.

On submitting the form first time, I get the following error:

Fatal error: Call to undefined method Perch::event() in /Users/simonclay/Dropbox/Clients/Arthur Edward/Website/Arthur Edward Website/perch/core/apps/content/PerchContent_Pages.class.php on line 39

I then press back on the browser and click submit again, this time I get the success message, and the form is processed as expected.

However, in Admin > Pages, I see that it has somehow created a new blank sub-page (with no regions) under the page that the form is on.

If I delete the page, I get the error message:

Not Found

The requested URL /perch/core/apps/content/<br /><b>Warning</b>: unlink(/Users/simonclay/Dropbox/Clients/Arthur Edward/Website/Arthur Edward Website//available-roles/): Operation not permitted in <b>/Users/simonclay/Dropbox/Clients/Arthur Edward/Website/Arthur Edward Website/perch/core/apps/content/PerchContent_Page.class.php</b> on line <b>143</b><br />/perch/core/apps/content/ was not found on this server.

Clicking back on the browser and refreshing the page list show the page is deleted.

But when I submit the form I get the original error again.

Here is my form template:

<!--detail-->     
<div class="col-md-8 job-detail">
    <h1><perch:content id="job_title" type="text" label="Job Title" required="true" title="true" /></h1>
    <div class="row">
        <div class="info">
            <div class="col-sm-4">Job Number: <perch:content id="job_id" type="text" label="Job Number" required="true" /></div>
            <div class="col-sm-4 text-center">Location: <perch:content id="location" type="text" label="Location" /></div>
            <div class="col-sm-4 text-right">Salary: <perch:content id="salary" type="text" label="Salary" /></div>
        </div>
    </div>
    <perch:content id="job_description_excerpt" type="textarea" label="Job Description Excerpt" html="false" help="A short description of the job for the listing page" size="xs" suppress="true" />
    <perch:content id="job_description_full" type="textarea" label="Job Description" html="true" editor="redactor" imagewidth="750" imageheight="500" />
</div>

<!--sideabr-->
<div class="col-md-3 col-md-offset-1">
    <div class="sidebar-box">
        <h3>Apply for this role</h3>
    <div class="widget-search">
        <perch:form id="job_application" method="post" app="perch_forms">
            <perch:input type="hidden" id="ref" value="<perch:content id="job_id" type="text" label="Job Number" required="true" />" />
            <div class="row">
                <div class="col-md-12">
                    <perch:input type="select" options="Mr,Mrs,Miss,Master" />
                </div>

                <div class="col-md-12">
                    <div class="error">
                        <perch:error for="name" type="required">Please add your name</perch:error>
                    </div>
                    <perch:input type="text" id="name" required="true" label="Name" class="form-control" placeholder="First name..." />
                </div>

                <div class="col-md-12">
                    <div class="error">
                        <perch:error for="surname" type="required">Please add your surname</perch:error>
                    </div>
                    <perch:input type="text" id="surname" required="true" label="Surname" class="form-control" placeholder="Surname..." />
                </div>

                <div class="col-md-12">
                    <div class="error">
                        <perch:error for="email" type="required">Please add your email address</perch:error>
                        <perch:error for="email" type="format">Please check your email address</perch:error>
                    </div>
                    <perch:input type="email" id="email" required="true" label="Email" class="form-control" placeholder="Email..." />
                </div>

                <div class="col-xs-12">
                    Upload your CV
                    <input type="file"></input>

                    <div class="error">
                        <perch:error for="cv" type="filetype"><span class="error">File must be a PDF or Office document.</span></perch:error>
                        <perch:error for="cv" type="fileupload"><span class="error">Couldn't upload the file - it may be too large.</span></perch:error>
                    </div>

                </div>  

                <div class="col-xs-12 hidden">
                    <perch:input type="text" id="type" antispam="honeypot" />
                </div>

                <div class="space-20"></div>


                <div class="col-md-12 text-right">
                    <perch:input type="submit" id="submit" value="Submit" class="btn btn-lg btn-primary" />
                </div>

                <perch:success>
                    <div class="success-message">
                        <span class="glyphicon glyphicon-ok form-control-feedback"></span>
                        Thank you, your application has been sent. We will be in touch soon.
                    </div>
                </perch:success>

            </div>
        </perch:form>
    </div>
    </div><!--sidebar-box-->
</div><!--sideabr end--> 

<perch:content id="slug" type="slug" for="job_title job_id" suppress="true" />

Perch is up to date
PHP 5.4.34 version is okay, but a little out of date. Consider updating soon.
MySQL 5.5.38 is up to date
Image processing available
SUMMARY INFORMATION

Perch: 2.7.2, PHP: 5.4.34, MySQL: 5.5.38, with PDO
Server OS: Darwin, apache2handler
Installed apps: content (2.7.2), assets (2.7.2), categories (2.7.2), perch_forms (1.8)
App runtimes: <?php $apps_list = array( 'content', 'categories', 'perch_forms', );
PERCH_LOGINPATH: /perch
PERCH_PATH: /Users/simonclay/Dropbox/Clients/Arthur Edward/Website/Arthur Edward Website/perch
PERCH_CORE: /Users/simonclay/Dropbox/Clients/Arthur Edward/Website/Arthur Edward Website/perch/core
PERCH_RESFILEPATH: /Users/simonclay/Dropbox/Clients/Arthur Edward/Website/Arthur Edward Website/perch/resources
Image manipulation: GD
PHP limits: Max upload 32M, Max POST 32M, Memory: 128M, Total max file upload: 32M
Resource folder writeable: Yes
HTTP_HOST: arthuredward:8888
DOCUMENT_ROOT: /Users/simonclay/Dropbox/Clients/Arthur Edward/Website/Arthur Edward Website
REQUEST_URI: /perch/core/settings/diagnostics/
SCRIPT_NAME: /perch/core/settings/diagnostics/index.php