I spoke too soon. It happened again tonight, the taxi signs disappear when in GSX I select "prepare for departure"
Doesn't happen here, see the attached screenshot. You haven't said which parking you started from in GSX, so I chose Parking 29 of the South Cargo area, which is close to the position you reported earlier.
I setup gsx at the airport so pushback is disbaled.
This will disable just the actual pushback, but not the parking preparation that would caused all GSX vehicles to appear.
I pressed "prepare for pushback and departure" and it said "have a nice flight" but all the pallets at the cargo ramp disappeared and so did the taxiway signs south of runway 10.
Although it's a bit unusual you would want to start a pushback after you disabled it, I tried doing the same, and no, after GSX says "Have a good trip" (without having done any pushback), nothing disappears.
Do I have to run the addon manager installer after the ord installer? I will try that once my flight is over.
You don't have to do anything, if you use the CURRENT version of the installer. As explained many times already on the forum, every scenery installer comes with everything needed for it to run, you only need to install the Stand-Alone Addon Manager if you want to update that one without downloading the scenery again but, if you ARE using the latest version of the scenery installer, you don't need to do anything else.
I still think there's something outdated with your installation.
Some of our sceneries have GSX remove automatically all ground details around a parking when you start GSX, but in order to do this, a scenery must be specifically programmed for it, and KORD is not so, lacking any special programming, preparing a parking for GSX won't touch ANYTHING.
Could be the problem is caused by an outdated FSUIPC instead ? None of our products use it or requires it but, if you have it installed because of another product, and it's outdated, it IS able to remove parts of our sceneries, see here:
http://www.fsdreamteam.com/forum/index.php/topic,9866.msg77709.html#msg77709