<<by using update statement i have corrected the username>> This looks very suspicious... Do we speak of an Oracle username as we can see in DBA_USERS? You cannot modify a username with a simple update...
<<I have confirmed that I need to make update with two tables only and corrected both>> Was this confirmed by Oracle Support? Please give us more details.
Maybe you have corrupted your data dictionary.
Note that when there is a space in the username you can still use it but you need to enclose in double quotes... But the best option is probably to create the "correct username" and to transfer all the objects, for example via datapump.
Are you talking about Oracle users or your application users? What tables and how did you update?
The correct way to "rename" an oracle user is
Step 1) Export the userschema
Step 2) Drop the userschema
Step 3) Import the userschema with a different name
Step 4) Make sure all the grants they were pointing to that user are still in place. So do this first on a test database.
I think I made a confusion here and sorry for that, I am not talking about Oracle user, here I am talking about application user.
But in this case we cannot help you: it is application specific and we don't know the application that you use... What does the application documentation state? Is your application an "in house development"? Maybe you can reach the developers, or a kind of support?