Do you mean you can not access your user content type configuration form anymore ?
Have you tried to restore a previous version of your content type ? You can access content type versions from the content type list by clicking on the archive icon in the column before the id.
"Oops! Template not found.. ;(" -> go on your content type, check template selection and save again
Settings of a content type are no more saved -> increase max_input_vars Apache variable on your server up to 3000 (it's about the number of field in the content type edition interface)
Same problem. In the Form & Content Type
no form field will not load. On each tab label Oops! Try to close the page & re-open it properly.
This happened after the update to version joomla J 3.3.5., After upgrades to J 3.3.6 the problem persists.
I tried to set the .htaccess php_value max_input_vars 5000 - did not help.
In gurus have some ways to resolve this problem?