On March 20th 2013 I upgraded to PRTG Network Monitor 18.104.22.1682. Starting the next day I started getting the following error on a sensor that has existed for months without any problems. The error is "Could not log in using the specified credentials. Please make sure they are not only valid for the target system, but for the probe system aswell. (Performance Counter error 0xB0000004)". I have searched the KB for this error number to no avail. I have tried rebooting both the probe server as well as the server that is giving this error. It just seems very coincidental that this started just after upgrading to a new version. The previous version before the upgrade was 22.214.171.12442.