I have written certain error messages under field section check.input.
in that check.input i have written like this
if update.status = add.set or update.status = modify.set then
if not before.update.check then
if <condition> then
else
message("message")
set.input.error("")
input.again()
endif
endif
endif
My problem is that for the first time it is validating the field. but when i m trying to change that field at that time the message is getting displayed but neither the set.input.error("") function is working nor the input.again() function is working.

i need this problem to be solved as quick as possible becuz by this problem i m not able to validate the data properly.

to my opinion this should work:
check.input:
if not <condition> then
set.input.error("message")
endif