I am having the same problem. I get the message
Welcome, you are about to install:
Deus Ex Revision downloadable content
This content requires 5.1 GB of disk space and will be installed to the base game location.
(Next 2 lines in red)
The base game was not detected.
Please install the GOG version of Deus Ex GOTY
after downloading the revision mod and trying to install. I tried installing Deus Ex in Program Files (x86)
but it made no difference.
I go on Galaxy and am told that it will download the mod again !
I object to being forced to use Galaxy to download/install updates. This sort of thing is why I do not use Steam
Why cannot the updates be available from the site without having to use Galaxy, and if we download
this mod from GOG why cannot we install it ? Also why should we be forced to run any game from Galaxy,
viz. Constantine_R post above.
Did you re-download Deus Ex GOTY and install another copy with that? You can try that if not. I have to have two installed copies of Deus Ex for it to pick it up. Weird how there is no difference in versions of my two copies that are installed, yet one works and the other doesn't.
Also, I don't use Galaxy and works fine now. You don't need Galaxy(I don't even have it).
They really need to add a manual search. I know of a few more folks having a lot of difficultly getting it to work because it simply can't find Deus Ex GOTY.