The
patch checks the registry to get the install path for the game. If it can not find that information in the expected format, that may be why it will not install. The end of the manual install procedure in the
Troubleshooting Tips topic contains a link to a registry file you should be able to use to get the patch working, and instructions on how to edit it if you did not install to the default path.
Unfortunately, the patch can not fix this problem retroactively, but there are workarounds to get back into sealed locations and replace any lost quest items that were on the ground in Verdistis (though it doesn't appear that you lost anything important). Either of the posts below will let you get back into the guilds.
FIX for the Missing Catacombs PortalTeleporting Anywhere, via hex editorI will have to reload one of my old saves to get the coordinates for the assassin's guild, and will update hex teleport post. If you want to use the catacombs post's file swapping procedure, I can also get the required data file.
Once you get into the guilds, they both have levers which open doors into the sewer, so you will hopefully be able to get back in again that way, if you need to.