Yes, I saved the order and created new one.
The problem is someone went and created a serial number in Iq01 with external number which is different from the profile assigned and sequence is last, When system tries to create a new serial no, it goes and checks the last serial number used and generates the next one in sequence. Since the last no. is out of sequence and it did not understand what to do and behaved weirdly. Let me know if my analysis is wrong.
Thanks