[TYPO3] frontend editing: moving content elements results in blank screen

[Bing Du]

Hi,

typo3 4.0.6

Frontend editing is turned on by page.config.admPanel=1 in the typoscript
template setup.  It works fine in general.  The only problem is when
moving content elements up and down by clicking the up and down arrows
respectively on the front end, the result is blank screen.  Other icons
(edit record, hide, new record after, delete) work fine.  Anybody else
seen this problem?  We have two typo3 servers both with typo3 4.0.6
installed and both have this problem.  What could be the cause?  I'd
appreciate any insight.

Thanks in advance,

Bing