Whenever I try to "Upload plug-in and archive to Steam." I am given a list of included assets, press 'Pack files' another window pops up with a progress bar and I receive the error 'Archive process failed' and the process cancels and returns me to the CK without uploading anything.

It seems we are also having the same problem in this thread http://www.gamesas.com/topic/1343897-problem-uploading-file-to-steam/

Same problem here

http://www.gamesas.com/topic/1343916-publishing-plugin-to-steam-workshop-problem/

Same problem. Still no resolution.

Ive been scouring the internets for the last few hours and still nothing. I dont know if the devs even know about it. It seems to only affect one .esp at a time and does not mean your copy of the CK is broken. I can upload different .esps but not the one I NEED to upload.

Same problem here. Still cant upload my biggest mod.