This problem has been annoying me and it only popped up recently. It never used to do this before, no matter how
many hours my play session was.

Before I post this on the Valve forums; I'd like to know if anyone else is facing this issue with Steam and Skyrim, or if it's just me.

Basically, after long hours of playing, when I want to quit Steam, an error comes up with something along the lines of "a Steam app still running, close that app first before quitting Steam" (not the exact words)... funny thing is, there's no such application running. Skyrim quit just fine, and I checked the task manager - nothing.

The annoyance? When this happens, Steam freezes for good and I have to use the task manager to kill the Steam process.

Bump. Still happening with lates patch.

you should post this onto Steam support forum

The only thing I can think of is that Steam Cloud is uploading the game saved files and you are trying to shut down before the transfer is complete.
Do you have cloud enabled under right click on game title ->properties ->updates tab click box to enbale or clear box to disable.

Yeah disable it. Than you will be able to turn it off almost imidiatly after you finish playing the game.

Steam Cloud has been disabled all this while (never turned it on, ever).

I'll try the Valve forums.

I haven't posted on the Valve forums yet, but I found out what was causing this.

GameOverlayUI.exe is a process that is somehow stuck running in the background after quitting a long session of Skyrim. If I don't terminate this process before shutting down Steam, it won't shutdown properly and Steam will hang.

I searched the process that is causing your Steam to hang and this website shows something that is NOT good.
http://file.net/process/gameoverlayui.exe.html
The write up states as a tracker/spyware. It further states that "This program is NOT a windows program".
With this info I would recommend a virus scanner and or a Malware scanner.

It's a Steam file, located in my main Steam folder. If it was malicious, Microsoft Security Essentials would have already picked it up.

Thanks for your concern though.

Good, just a thought. One thing you could try. I'am thinking outside the box - but when you shut down the game try exiting to main menu before going to the desktop. Maybe theres something in there it has a hard time shutting down if you go from game directly to desktop. Try it out and let us know.

My steam cloud is disable as well as the update games automatically function for everything in my library and non of that seems to matter to the steam client. The options are there but in my case and I am sure others they don't take. Steam always updates to the cloud if I am using it online and games autopatch regardless of properties settings. I tend to run Steam offline when playing Skyrim unless I want to ensure that an achievement goes through(Please continue, my good sir. I am an achiever)

I've notice the last few weeks that Steam has been really slow to wrap things up when I quit the game. svcks a ton of bandwidth (I only have 3 GB DSL) and takes about ten minutes to do its thing with the cloud.

Yes because with the new version of Steam that was released in mid to late Feb, Steam cloud is enabled by default. You have to manually go in again... and turn it off.

Yep and that is exactly what the file is a tracker that is installed by Steam that tracks your usage and reports back to track your game play usage so they can give that info to the developers and other third parties.