What to do if the logon for a Digital Signature fails under Windows XP?

This applies to Windows XP only. If to try to enter a digital signature for a measured result in the database browser, the system displays "illegal password", but your password entry is correct.

Before proceeding to the solution: If the account you are using for the digital signature is different from the one just logged in, please make sure the account and password is valid by logging in to the computer with that account and password. Then return to the previous user account.

Solution: There is an MS Windows XP registry value under the key:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Lsa\ForceGuest