You may or will need to add UO information to your registry for everything to work.
I in no way take responsibility if you screw up your computer, windows or registry
Example:
Windows Registry Editor Version 5.00
[HKEY_CURRENT_USER\SOFTWARE\Origin Worlds Online\Ultima Online\1.0]
"Upgraded"="Yes"
"ExePath"="C:\\Games\\Electronic Arts\\UO\\client.exe"
"StartExePath"="C:\\Games\\Electronic Arts\\UO\\uo.exe"
"PatchExePath"="C:\\Games\\Electronic Arts\\UO\\uopatch.exe"
Just replace the path with the location of your UO install. (yes the double \\ are required)
This is saved to a txt file, then rename .txt to .reg and double click to merge it.
possibly for a registry file to take full effect you have to restart your computer or log off and log on.
If you don't have have a registry entry in "SOFTWARE\Origin Worlds Online\Ultima Online\1.0" Then the Ultima.dll will not be able to detect that you have an installation of Ultima online on your computer.
If you can open RegEdit. go to Edit > Find (crtl + f ) and type in client.exe, make sure all the boxes are checked, except match whole string only. click find next. Then press F3 until you find a valid registry entry for an ultima online install. make note of all the locations you find one. If the place I listed above is not one of them. Then you'll need to make the reg file and merge it just like I describe.
Ultima.dll is old and does not recognize the new installation locations. From my testing it is not possible to swap it out with the newer openuo dlls.