When executing your custom script from a Windows monitoring station using a .bat file you may find that the following items need to be addressed: Ensure you have echo off in your .bat file.
If you are using a "does not match" threshold comparison, try switching to a "does not contain" threshold comparison as this typically produces better results.
The Uptime Infrastructure Monitor string check will check only the first line of output for your message so ensure that the status you are looking for is in the first line.