The "Sign Check" or digital signature error in typically occurs when your security software blocks a license validation check or when specific core files (like DotNetCommon.dll or DTUltra.exe ) have been modified or replaced, causing a signature mismatch. Common Fixes for "Sign Check" Errors License checking error - DAEMON Tools Forum

If Test Mode works but you need a permanent solution without Test Mode’s watermark, disable signature enforcement via Group Policy (Windows Pro/Enterprise only).

If the latest version suddenly shows the error, it may be a bug in that specific build. Many users report success with or 4.x .