Exception: Cannot create the AMA sample mapper to play this clip

I am running Media Composer 6.5.3 on a PC.

My rushes have been shot on XDCAM 23GB Sony discs and I have a Sony PDW-U2.

I usually put the disc into the PDW-U2 and the clips appear in a bin in Avid.

Then I select them all and transcode them to a chosen resolution.

This has worked for at least 18 months now, but today I keep getting the "Exception: Cannot create the AMA sample mapper to play this clip" error.

I recently upgraded to 6.5.3, but that was over a month ago and everything has been fine since.

Has anyone any ideas of how to fix this?

Thanks.