I had the same problem with my another e-mail address but it unsubscribed successfully now.

There are two ways for that.

First one: Check up your tool box that located on the top in the message box (just click the Tools). If it is on (rich-Text Editor on),you must off this box (rich-Text Editor off). Then try to unscribe again (subject line is must blank, type SIGNOFF MUSEUM-L in the body). SIGNOFF MUSEUM-L must be capital letters.

Second one: Go to Google.com then search the MUSEUM-L (usually located the top on the list). You'll find the MUSEUM-L site, then click the join or leave the MUSEUM-L list (or change settings), and type your e-mail address and your name in the box that prepared, then click the leave MUSEUM-L List.

 After that, you must check up your e-mail for unsubscribing. That's all. If you successfully unsubscribe MUSEUM-L, would you let me know? My e-mail address is [log in to unmask]. Bye.