DPM 2012 has run out of disk space

Hi,

I'm relatively new to DPM and have run into a problem.  It appears that the DPM server has run out of disk space and has the following error:

DPM has run out of free space on the recovery point volume and will fail synchronization for H:\ on SRVFS02.FILECLUSTER.osfc.ac.uk in order to prevent existing recovery points from being deleted. (ID 30195 Details: Internal error code: 0x80990AB2)

Is there a way of freeing up some disk.  It appears that it allocated space which has run out but the disk space is fine.

Any help would be very much appreciated.

-Scott