Mountain Lion keeps logging user out...

hmm it appears that the common trend is here Mac pro with dual grapics. That said, are you guys still using the graphics card that came with that machine or has it been removed and replaced by a new graphics card?can you post your graphics card here in the trend?ALL of it as long as its attached to the mac pro

I am having this same issue with my iMac (2008 or 2009, I can't remember). It will randomly restart. All factory hardware; no upgrades.

Edit: This may be the problem: http://support.apple.com/kb/TS4348?viewlocale=en_US&locale=en_US

Happening to me as well.

Mid 2010 Mac Pro 2.8 Quad Core with 2 ATI Radeon HD 5770 1024 MB graphics cards. Note that one is a PC version flashed to Mac compatibility.

I had this problem with Lion, pulled the flashed card and ran just on the stock ATI for a week. Put back in the flashed card and no more crashes.

If I am not using spaces, like sweeping with three fingers to go to another space, but stay in the same space all the time, I am not logged out. Have anyone else noticed this?

As for my case, I know for a fact that this doesn't prevent restart because I will walk away only to come back to find my computer restarted.

I'm having exactly the same issues. Mine seems to log out when I'm not using it, even though it's set to not go to sleep. After some inactivity, it seems to log out

This is my setup:

Mac Pro Early 2008

Processor 2 x 3 GHz Quad-Core Intel Xeon

Memory 28 GB 800 MHz DDR2 FB-DIMM

Graphics ATI Radeon HD 5770 1024 MB

My Macbook Pro doesn't have the same problem under Mountain Lion.

Don't know if this helps anybody?

Symptoms

After upgrading to OS X Mountain Lion, your Mac may keep returning to the login window after you have logged in.

Resolution

You may have an incompatible startup item in your user account. You may need to start the computer in Safe Mode and disable login items by using the following steps:

1. Shut down your computer.
2. Wait 30 seconds
3. Hold down the Shift key after pressing the power button.
4. When you see the gray Apple logo and progress indicator (looks like a spinning gear), release the Shift key.
5. If you are prompted to log in, type your password, then hold the Shift key again when you click Log in.
6. Choose Apple () menu > System Preferences.
7. Click Users & Groups.
8. Click your account name, then click Login Items.
9. Look for any application that has a prohibitory sign (a gray circle with a slash) over its icon. This indicates an incompatible item.
10. Select the incompatible login item, then click the Delete ➖ button.
11. Restart your Mac.

I have also just been digging around System Preferences and found this:

System Preferences, Security & Privacy, click 'Advanced' button at the bottom, uncheck 'Log out after 60 mins of inactivity' (you may need to click the little padlock bottom left to change settings)

I'm trying that and will report back, but looks promising. Although doesn't account for it mostly being present on Mac Pros.

Just also checked my MBPro, and it wasn't checked, so this might be my issue.

Thank you jonnygreen65!!!

You have FINALLY solved my problem!!

Must be a bug that sets it to 'On' on some machines I reckon.

My system is a Mac Pro 2 quad core Xeon with dual NVIDIA GeForce GT 120 video cards.

I don't have to be using the system when it happens. I come back and sometimes it has done it on its own.

I can't believe I'm actually thinking of going back to Windows. This is one more thing in a long series of events that demonstrates that Apple is slowly over time producing half baked products and no quick responses to remedy the situation.

I wish they'd use some of that $98 billion and put it to good use!

I did a clean install and it still happened, to I looked at startup items in safe boot, none were indicated as incompatible. I also checked the security time out, but it wasn't checked. So I don't think it was either of those issues.

I decided to run both monitors off of a single card, and I am not getting any logouts after a couple of hours. This is doing the same things that were causing log outs every twenty minutes or so.

I really think that the sudden log out while working, NOT the log outs when leaving the computer for a while, are caused by multiple video cards.

Well, I have been running it now for about 3-4 hours with Photoshop, Lightroom, Safari, Email, Plex Streaming, flicking around between spaces rapidly (which seemed to trigger the logouts before) without being logged out once.

Did you have to physically remove the card from the machine for this to work? Or was unplugging the monitor from the card enough?