I got a wish listed book this afternoon. I requested it. About an hour later I got a message the book can't be send. Reason -loaned the book to a friend and don't have the book anymore.

Just offhand, I'd say the first person who received your request either didn't send it off on time or mark it mailed, and the system passed the request to another person who sent you the message.  

This means the first person who sent you the book doesn't receive credit for it. You can check with the PBS staff to see if this happened, and, while you are not required to, you can still award a credit to the member who sent you the book.

This is why I mark a book as mailed as soon as I put postage on it. 
My mail box is right next to my front door - if I place it out there for pick up then it's mailed. Even if the mail man/lady has already been by that day and won't be around til the next day, it's still mailed.

I've had 3 maybe 4 books in the last 10 years, that arrived and were never marked as mailed. I had to go thru my Transactions to figure out how to give credit to the right person as well as go to my Wish List to remove the title that had been added by PBS because it had timed-out and there were no other copies currently in the system - this was bothersome to say the least.

Some folks are just forgetfull that way.and it becomes a 'minor' problem for others. Even worse would be to get two of the same titles because the 1st one forgot to mark it as mailed and it timed out and the 2nd was quick as a rabbit and got it out the same day as they got the request - yowza.
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ETA - Charles, check the name / address of the wrapping and then check your Transactions File for that title - you might find several with an "X" in the RH Box along side of the title indicating a canceled transaction - click the 'Detals" link on the LH side to figure out if that transaction is the one you received. If there is/are no other copies in the system you may also want to look at your Wish List to make sure it was not added. You also may want to look at your "Main Page" and make sure it is not on your "Books I've Requested" or books "En Route To Me"  - Iff its on your "Books I've Requested" then cancel before you get another book - If it's listed in your "En Route To Me" then don't mark your current copy as received until you double check where it was sent from and check with the address of the one you just received.
You may end up with two books. 

Good Luck with the mess . . . 

I think Charles meant that he got offered a wish list book and he accepted the offer (i.e. he requested the book). Then the request was declined because the other member had loaned it out.

That happens sometimes. People put their accounts are on hold and then somebody wish lists a book they have on their shelf and by the time they come off hold and it gets offered to the wisher, they've given it away. Or they have the book out and post it, then before they can respond to the request a friend comes by, sees the book, and asks to borrow it. 

heh . . . .
(Cathy) I think you might be right - I just read the "I got a wish listed book this afternoon." as if the mailman/kady had just delivered it...
I've gotten several Wish Listed book offers this year that never panned out. All my WL books are on Automatic Request so as soon as one is posted and I'm next in line it gets ordered. So if someone posts a WL book it should go directly to their 'hold' list and 'sit'there for the 1-hour grace period.
How someone can post a WL book and then decline an hour later is unfathomable - which as Charles indicated is very odd indeed.  

I've received offers for WL books, accepted them, and then five days later they've been cancelled by the system because the person who offered them didn't respond.  Sometimes it happens - I figure they probably listed the book, found out a family member or friend wanted it, and just let it work through the system rather than cancel.  That's happened at least twice.  It's no big deal to me, because I go back in the FIFO line and don't lose my place, so it will show up again eventually.  I'm pretty laid back about these things, I guess.

How someone can post a WL book and then decline an hour later is unfathomable - which as Charles indicated is very odd indeed. 

If your shelf is On Hold, and you add books to your bookshelf while it's On Hold, they get posted when you come off Hold. If you didn;t realize that some of the oboks you were posting were WL, then it could be days or months later that you come off Hold and they all get offered to whoever is in line.

I've had this happen A LOT.  Someone posts a WL book and my WL is on auto request, so it goes to me (I'm first or only on a lot of books).  Then nothing...the WL book is never mailed, the poster never messages me and the request times out.  There is one book that has been posted THREE times by the same person, I am the only wisher and they have let it time out every single time. It is very frustrating. 

Yep, I got offered a book and accepted the offer and then the member wouldn't send the book as I post all my requests with conditions, one being the book be as close as possible to original and not a "dumbed-down" adaptation.  The member said they are not accepting books with conditions on them at this time.  The book in question did happen to be from a series released in both original and dumbed-down versions and I have bought volumes and got them home before realizing it was the wrong version.