There have been more than a few instances where carriers have gone out of business and left behind transfers on to their accounts that can no longer be processed. Sometimes you are lucky enough to get a warning before all is lost. One of the signs that should not be ignored is if the carrier's pallet accounts are made inactive by the pallet hire companies. This can happen if the carrier does not pay hire hire invoice. If the transfers you have raised to the carrier cannot get processed then you need to immediately stop transferring more pallets to the carrier's account.
You could then work on a strict exchange basis with the carrier or you could transfer direct to the end receiver. You could also decide to use a different carrier.
If you have transfers outstanding then you could ask for the carrier to dehire the pallets off your account or return them physically to you. Either way, you should not let this problem continue for very long.
A good first step is to discuss the situation with the carrier and then decide what to do next. It might be a short term cashflow problem or it could be something more serious.