Looks like you are talking about the FRAMEWORK_5_2 branch, not the 
master branch. Duplicate of bug #14111 which never was backported.

Trying to delete an attribute of type 'image' results in the error 
message shown below. It is not a permissions problem as it also occurs 
to the administrator. I could not find the classes mentioned in the 
message.

(BTW: the image did not get displayed in the first place, I shall file 
a separate bug for this)


Fatal error: Class 'DeleteAttributeDescForm' not found in 
/usr/local/www/apache24/data/whups/admin/index.php on line 968
Ein schwerer Fehler ist aufgetreten:
Class 'DeleteAttributeDescForm' not found
in /usr/local/www/apache24/data/whups/admin/index.php:968

1. Horde_ErrorHandler::catchFatalError()

Details
Die vollständige Fehlermeldung wurde in Hordes Logdatei geschrieben 
und für Administratoren weiter unten ausgegeben. Benutzer, die keine 
Administratoren sind, bekommen diese Details nicht zu sehen.

ErrorException Object
(
     [message:protected] => Class 'DeleteAttributeDescForm' not found
     [string:Exception:private] =>
     [code:protected] => 0
     [file:protected] => /usr/local/www/apache24/data/whups/admin/index.php
     [line:protected] => 968
     [trace:Exception:private] => Array
         (
             [0] => Array
                 (
                     [function] => catchFatalError
                     [class] => Horde_ErrorHandler
                     [type] => ::
                     [args] => Array
                         (
                         )

                 )

         )

     [previous:Exception:private] =>
     [severity:protected] => 1
     [logged] => 1
)