login failed for user error 18456

hi,

i have installed and configured SQL 2008 R2 and all seem to be working apart from a strange error I receive in the SQL logs.

I created an SQL account with sysadmin privileges but but for some reason i get the following error every few minutes.. login failed for user username Reason: Password did not match that for the login provided [Client:<Local machine>] error 18456, Severity 14, State 8

Any ideas why i get this message... i have checked the password

Thanks