Maybe a year ago you guys were using a different version of Lazarus/OS. Try the older version first and see if it works.
You did not tell us much here, like what OS, FPC, Laz.. etc? and most imporant the code this form is running.
You would work on this logically. Remove events one after the other, like OnCreate.. and see when the problem disappears, then you check the causing event procedure.