When the Sql server instance is differ from the machine name, this error will be given as a result of verification tasks under the system check of CRM installation. Most of the time this happens if the Sql server instance changes after the first installation and reinstallations.

Anyhow this can be fixed easily as we can use few sql stored procedures. Follow the steps listed below.
1. Open Sql Server Management Studio, get a new query window and execute “SP_HELPSERVER”. This will show the different names of Sql Instance and the Machine.
2. Execute SP_DROPSERVER [SEVER NAME] — “name” column from the result of SP_HELPSERVER execution
3. Execute SP_ADDSERVER [SEVER NAME], local — “computer_name”\”network_name” column from the result of SP_HELPSERVER execution
4. Execute SP_HELPSERVER to check whether the two names are identical
5. Restart the MSSQLServer Services, and recheck the conditions.