IUSER_SERVERNAME logon failure

I need help, my system log keeps getting full due to constantly getting the following error message: THE SERVER WAS UNABLE TO LOGON TO THE WINDOWS NT ACCOUNT IUSER_SERVERNAME DUE TO THE FOLLOWING ERROR:
LOGON FAILURE: UNKNOWN USER NAME OR BAD PASSWORD. THE DATA IS THE ERROR CODE –
this is all that appears in the data section: 0000: 2e 05 00 00 —-
Note that servername was substituted for the name of the server
Why is this happeneng and how can I fix it????