List validation based on the user logins

http://sourceforge.net/forum/forum.php?thread_id=2959693&forum_id=549512

try the following:

AD_Ref_List.Value NOT IN (
case when (@AD_Role_ID@ = 100021)
then ''
else 'Perm'
)

You have to understand how it works:
-your statement was: if role is 100021 then no value is allowed, for other roles only "Perm" is allowed. So I guess your description was wrong: when you login with 100021 the drop-down list is empty, otherwise only 'Perm' is shown
-my statement is: if role is 100021 then no values are excluded, for other roles 'Perm' is excluded (it matches with your original requirements)