SignTool.exe Sporadically Fails with Exit Code 1

I strongly suspect a failing connection to the timestamp server being responsible for occasional failures. Perhaps you check your system event log for lost connections at the time in question.

I had the same problem. It happens because MS antimalware process MsMpEng.exe check the binary and don't let anyone access it. To solve the problem, I build binary on RAM disk and it worked.

I've just into this issue, on Windows 8.1, so it's not the Windows XP root certificates issue that some folks cite.

I found that the problem was caused because the .exe being signed was also running.

If you run signtool from the cmd prompt and try to sign it you will get a helpful text message telling you what is wrong (so much better than the return code 1 from CreateProcess().

Stopped the running process and was able to sign OK.