Attention: If you are using flexfields server-side validation, you cannot use form field references (:block.field). You must either remove your field references or turn off flexfields server-side validation using the profile option Flexfields:Validate on Server.
Flexfields:Validate on Server
Attention: You may not use a DISTINCT clause in any of the column fields or in your WHERE/ORDER BY clause (you should use a view with a GROUP BY clause instead of your actual table).
If you are using a validation table with special arguments such as :$FLEX$.Value_Set_Name for your value set, you should specify No in the Enable Security field, since any security rules you have for your value set would ignore the values of these special arguments, and your rules could have effects other than what you intend.
Overview of Implementing Table-Validated Value Sets
Values and Value Sets.