Under the task properties, do you have the "Run Whether user is logged in or not" selected?
Yes, it is selected. I should have mentioned that. I also tried checking "Run with highest privileges" to no avail. CPU mining works fine without the latter checked. Also, in this case, I'm trying to run it while the user is logged on anyway (right clicking on the task and clicking Run), but it fails. I'm only guessing that the process can't access the video card. I always get either two errors or two infos immediately (the task either fails to start or "completes successfully").