Just patched and dicked my UoS due to a memory shortage just posting in case you run into the same problem
Getting a Windows Virtual Memory Error when starting Ultima Online from UOSteam?
1. Download: LargeAddressAware.exe
Open the Program
2. Select an Executable -- Select client.exe in your UO install directory.
3. Check Box the Large Address Aware Flag!
4. Click Save. Restart UOSteam and it should open Ultima Online fine.
Info ripped from http://www.runuo.net/forum/forum/runuo- ... windows-10