if you create account via web. go to your MSSQL open database with account and check that account is crated. If yes then probably you enter wrong ID (login) try change your login in database if contain capital letter:
Example:
Test change to test
then try login to game.
next step what you can do is check different password
Example:
Test123 -> 68eacb97d86f0c4621fa2b0e17cabd8c
test123 -> cc03e747a6afbbcbf8be7668acfebee5
test -> 098f6bcd4621d373cade4e832627b4f6
Test -> 0cbc6611f5540bd0809a388dc95a615b
its probably some problem is inside the database, that you can crate account with various login and pass but when you try login system not recognise this information what you giving.