Hi Tasneem,
just to clarify:
the action you run is a normal from.scratch hiring action? Or is it a transfer from recruitment to personnel Administration making a candidate an employee?
You say, you get the error, when you try to change data in IT0006.
You you get the same error, when you create a new infotype 0006? And if that works, can you change that particular record?
it's quite weird and looks like somebody might have messed around with fundamental settings. One thing to check would be table T777D. For IT0006, it should look like this:
kind regards
Sven