You don't do anything wrong so the problem must be some other mod file(s) that have remained in your directory and you have to remove them. Especially mod files of the type "movie" are not shown in Mod Manager since the don't need activation (as the ACW pack files) so check carefully your data folder.
Also check to be sure that there is a folder named ACW in data/campaigns and in there is startpos.esf among other files. If everything seems o.k. re-download the mod in case of a corrupted download.