I know it is too late for this, but hope it works for other visitors:
Taken from the address: http://bit.ly/jLU0ft
Expression Encoder v4 from MSDNAA and DreamSpark incorrectly limited the screen capture on some PCs to 10 minutes. To fix this issue, download and install an updated version of the English Expression Encoder from http://bit.ly/EncoderFix. This free Expression Encoder should be installed over the current English version of Expression Encoder v4 Pro product obtained from MSDNAA or DreamSpark. Do NOT uninstall the older version.
You can verify that the install has succeeded by noting the version number change from 4.0.1639.0 to 4.0.1651.0.
This fix is only needed for the English version of Expression Encoder v4 as the localized versions already have the fixes mentioned below, so there is no need to upgrade them.
2 problems resolved in this update of the English Encoder v4 package are:
Pro/Pro without Codecs SKUs incorrectly limited to 10 minutes of screen captures on some PCs.
XESC files not being able to be played back in Windows Media Player on the 64-bit version of Vista and Server 2008.