Acces Denied when running set-aduser and delegated rights

Hi,

when a user with delegated rights run a script to change an specific field he gets the message access denied.

If he changes the value over the ADUC snapin, he can change the field where he has the rights.  

if ($objext2txtbox.text -ne "") {set-aduser -Identity $user.DistinguishedName[0] -Replace @{employeeNumber=@($objext2txtbox.text)}} else {$user.employeeNumber.clear()}

Above the codesnip where the change will be set. If the complete code is required i can post that one too.

Best regards

Malte