Error 500 when submitting to adopt a Hewan (pet)

This is the page in question:

What the error looks like:

And the error message:

<title>Error 500</title>
<font size=4 face="arial">Error 500 :(<br><br></font>

<span style="font-size:8pt; font-family:arial; color:#000000;">
<p align="justify">An error occurred.</p>
<p align="justify">If the problem persists, probably the application you use does not work correctly, because someone is working on it, or because there is a problem in the application. In the latter case <a href="" target="_blank">contact us</a>.</p>
<p><a href="javascript:history.back()">Go back</a></p>