In the directory assets/snippets/maxigallery/templates/ there should be a file managebuttontpl.html with the content
<form action="[+maxigallery.urlaction+]" method="post" name="activateadminform">
[+maxigallery.hiddenfields+]
<input type="submit" value="[+maxigallery.strings.manage_pictures+]" />
</form>
This can be overwritten by some other chunk using the parameter &manageButtonTpl.
Check if your MG call makes use of this parameter.
