Hello Sourabh pai,
First go to T.Code: FBL5N and see the open items of the customer.
In those open items check if any of the open item is over due or not, if any those items are over due then only system will give the error message.
Also ensure the right risk category is assigned in the FD32 of that customer master.
If you are frequently changing the settings and check then execute this program "RFDKLI20/RVKRED77/RVKRED88" in SE38 for reorganization of the credit data and then run the cycle.
Regards,
S.Himavanth.