a friend of mine has this specific problem and after trying the proposed solutions from the "common issues" topic over and over again, I've decided to open a new one.
First: He owns the 17 in 1 Command & Conquer Pack in the origin version, which initially caused a launcher issue to occur, which we worked around with the launcher fix link provided in another topic and with administrator mode etc.
This works perfectly fine, but: only in English. As I've read, this giant pack is ONLY available in English, so we figured it out to obtain a language pack for him, since he's not that fluent in English.
That's were everything went down the sh*tter. The German language pack caused the same error as the Steam Version does when trying to use C&C Online: "CA public key patching routine failed" and we're not able to get rid of it, by any means.
A quick summary: I've read the "common solutions" thread, countless times. The error itself seems to be known, but only with Steam. His Antivirus isn't blocking anything, he runs the game & launcher in administrator mode as well as in Windows XP compatibility mode. We've downloaded the launcher fix for the 17 in 1 pack and last but not least installed a German language pack.
Has anybody ever had the same issue?
Thanks for the help beforehand.