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This is not addon problem, this is files system permission and file read/writing issue. It may come from some security plugin or from wrong configured file system owners. in any case I recommend delete the addon. Then connect via FTP or cPanel file manager and delete addon folder. The error says WordPress can't fully delete it. S you should delete it manully. Then upload and install it again.
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Will this delete my users attachments that they have uploaded?  Or will everything just slide back into place like it never happened?