If there are read-only files in an archive, it will have problems with Wrye Mash. Either the modder should change that, or Wrye Mash should be changed to either ignore the read-only attribute or automatically remove it. The way Wrye Mash works, it uses temporary folder where it extracts files, and then tries to remove those temporary files, and it "chokes" since it cannot empty the temporary folder if some files are read-only. I know at least one mod which also has this problem, it is called Souly Soulgems, link is: http://planetelderscrolls.gamespy.com/View.php?view=mods.detail&id=5161
Another thing that some modders forget, which does not seem to bother Wrye Mash, is the inclusion of "thumbs.db" file in their mod. It is a file which is generated automatically by Windows if a folder contains image files. It is actually hidden, read-only and system file, which contains data of thumbnail images when you view the folder in Windows Explorer, and if you have thumbnail view active. Creating that file can be disabled from folder options. In any case, it is completely unnecessary and it only works in the modders system, not in anyones else. I don't know which Windows versions create that file.