Can you tell me please? :) Teach me your ways, ElkArte :D
Check the error in elkarte log and you will find more about the error. Without the log from elkarte is impossible to tell what is wrong
Do youmean you want to change the text of the error to something else?
If so, the text is in... Ouch, I forgot, it should be in themes/default/languages/english/Errors.english.php