Why did I get a message saying my Commonwealth Catalog request is unfulfillable?
Don't even bother asking for items that are new. Most systems won't send their new items until they are about 6 months old. This is to give their patrons first chance at the items.
There are several libraries -- especially some small libraries in the CWMars consortium -- that are open very few hours or are only associate members of the consortium. If the item is in such a library, it may not be processed in the five day time period or at all.
Materials that have holds on them will not be chosen to fulfill Commonwealth Catalog requests by the owning system.
Some libraries have had more than their share of technical problems that might prevent them from filling the request in the 5 day limit.
Also sometimes when someone goes to look for the book or item, it turns out to be missing. There is no way for anyone to indicate this in the ComCat software.