China Demands Removal of Artifacts from Silk Road Exhibit...

The "Beauty of Xiaohe". Image from Penn Current.
Buried circa 1800 BCE, one of approximately
500 mummies excavated in the Tarim Basin
over the past 40 years.

...that it had agreed to be exhibited in the ground-breaking exhibition.  No explanation was given for their demands.  The host museum (the Penn, in Philadelphia, Pennsylvania) complied with the demands and have withdrawn two Tarim Basin mummies from the exhibit (they would have been a HUGE draw), along with some 100 rare artifacts never before seen outside of China.  Evidently China has thrown another hissy fit for reasons that only it knows (but we can make some educated surmises).  The Penn people aren't talking.  What was to be a block-buster exhibit that presold thousands of tickets will now have that money refunded and a much reduced exhibit, with photos of the missing mummies and artifacts, offered instead.  The reduced exhibit will be open to all visitors ot the museum who pay its general admission.  The exhibit - with mummies and artifacts - has already been viewed at the Bowers Museum in Santa Ana, California and the Houston Museum of Natural Science before the final exhibit at the Penn Museum. 

Story at Pasthorizons.com
China demands removal of mummies and artifacts from Silk Road exhibition
February 3, 2011

Some possible hints about why the artifacts and mummies were pulled at the last second by the Chinese government (who conveniently turn blind eyes to the concepts of  "contract" and "rule of law") may be found in this article at the Los Angeles Times:

China thwarts 'Silk Road' exhibition in Philly -- and Bowers Museum could be out $27,500
February 3, 2011 | 10:38 am

February 2, 2011, 2:54 pm
China Asks Penn to Remove All Artifacts From ‘Silk Road’ Exhibition
By RANDY KENNEDY