Sorry to further add to the necro bumping but GOD. BLESS. this thread and you guys. I was going nuts trying to figure out what was happening.

I'm glad that this thread is helping others as much as it did for me ;)
Even two years later, I'm still so grateful to all people who helped :D

Rundll32 uses up my CPU even after I've quit the game.

I think I've had this problem before with a physical copy of an old game I bought. I remember how I uninstalled the game and then turned my computer off and on again.

After this, my computer didn't have any issues with CPU usage. So I did the same thing with this game, and Rundll32 could no longer be seen in the Task Manager.

Here's my plan:
Step 1: Uninstall the game.
Step 2: Turn off computer.
Step 3: Turn on computer.
Step 4: Reinstall the game.
Step 5: Play the game.
Step 6: After quitting the game, go back to step 1. Repeat the cycle forever.

Is this considered to be a solution? Or am I doing something bad to my computer by doing this?

Is this considered off-topic? If so, apologies.

A big thank you to this thread! :-)

UT2004 has been running at a crawl of late (and not starting on first run) and the problem was also killing the wifi connection to my router. It only started happening q. recently too so I'm guessing M$ have shut down the "service" which the games explorer tries to connect to..? I suppose it could also be an update which caused the built-in firewall to block the DLL from accessing the service. Does anybody know?

Yep, it was closed... and it was removed in Windows 10 build 1803

Can confirm: Thanks to the info in this thread, I can now play the Serious Sam games (again) on my Win 7 box.

@Splatsch, @Hypersomniac & all -> You're awesome! Thank you.
Microsoft -> Yeah, not so much. (Top-of-the-line product life cycle management. Not.)

This thread should probably be pinned by GOG, since it seems like it's a problem that's affecting more people lately (including me), and is specifically related to older games.

The problem with this fix is that it will fix problems with older games, but will simultaneously cause problems with newer games. You will get a new error message that says "Failed to create the GameExplorer object."

The original version of Bioshock is an example of a game that will not launch when this fix is applied.

Hooray, fixed this crap! I ran into it months ago with the original Guild Wars but didn't realize it was Windows' fault until trying to play UT99 just now. I renamed the gameux.dll files in both SysWOW64 and System32 and the issue seems to be fixed. Fuckin' Windows man.

Edit: Oh, I only use the basic Windows firewall and Windows Defender and have for years, so it's not just a third-party firewall issue.

Very weird how this thread (re-)surfaced just a day after I solved my own problem with gameux.dll and rundll32.
It was taking up a constant 10% of CPU usage.
Enabling the command line column in Task Manager revealed that it was Star Wars Battlefront that tied it up.

I needlessly downloaded Process Explorer to try to kill the handle, not wanting to touch rundll32 itself, but that didn't solve anything. Killing the rundll32 process itself did though. Maybe just a temporary fix, until next time I launch it.

-> https://www.gog.com/forum/general/old_games_not_launching_and_eating_100_of_the_cpu_on_windows_7/page1

Thanks!

I went through that and that guy basically says renaming the gameux.dll file to anything other than that name works for him. I renamed my files to gameux.dllNO (both in the sysWOW64 and System32 folders to make sure....)and it worked for me too and now Juiced and Emporer Rise of the Middle Kingdom start on first go instead of two goes! I heard this would break newer games but I'll deal with that later when I come to it....probably rename them back or something....

I had tried the registry method earlier but that didn't work....there was another method I tried too but I forgot what it was, and that didn't work, it was only renaming the files that did it for me.

Now to figure out why Juiced crashes on test drive mode....

There doesn't appear to be a fix unless gog decides to sell this game and run into this same issue and fix it up themselves....