First of all sorry for my English, I hope to make myself clear
I'm trying to upgrade a 3.1 instance to 3.4 (not 3.5 because a plugin is not compatible). After uploading all files, in the plugins check page, I get an "unavailable missing dependencies" error, regarding the webservice_rest plugin. I think I've spotted the directory where it is located (admin/tool/mobile) and tried to re-upload the files several times, but I can't get rid of that error. I also tried to re-upload the admin/webservice directory, to no avail either.
I seem not to be able to find any suggestions anywhere, so I'm asking here.
Thanks in advance