Well, so far, we are unable to get enough information around this topic on our WindowsUpdatesOnline.com Forums. Some security program like Trend Micro Antivirus had no help on this prog.dll. This is ok, anyway.
First, that prog.dll file might be safe if it occurred when your system was busy, when you try to run another installed project on your PC, or after you removed some 3rd-party program. Please be educated that, some imperfect program's own uninstall module would be able to delete some shared items in your OS, with or without alerts. If this is your case, please repair or reinstall related software, service by using the Admin access.
2nd, it too is common that some malware can hijack some important Windows resources, such as kernel32.dll. Then your up-to-date AV could help address such problems the efficient way.
Well, I will admit that all other dll or exe related errors are the most troublesome items for Windows users.
* Get instant help at http://malware-removal.windowsupdatesonline.com/
* See or review the original query around the said prog.dll error on Yahoo Answers: https://answers.yahoo.com/dir/index?sid=396546062
P.S.: Please feel free to comment on this topic with more meaningful input and/or accurate screenshot/ img, etc. Thanks and TIA!