Not asking about the login you are using to SQL Server. Asking about the account that SQL Server runs under.
The file name you're specifying has no extension. Go to that folder on the server and make sure that the file there also has no extension (remember windows hides extensions by default). Don't guess, access that folder on the server and check exactly what the name is.
Gail Shaw
Microsoft Certified Master: SQL Server, MVP, M.Sc (Comp Sci)
SQL In The Wild: Discussions on DB performance with occasional diversions into recoverability