The CDS control room main file server developed a problem at 19:30 Wed night and went into "read-only" mode. Reboots at 10:22 this morning cleared the problem. 
For future reference, here are the three emails it produced at the time of the problem

May 25, 2011 07:30:05PM - Controller 0
INFORMATION - Cache synchronization completed: unit=0

May 25, 2011 07:30:06PM - Controller 0
INFORMATION - Enclosure added: encl=0

May 25, 2011 07:30:33PM - Controller 0
INFORMATION - Enclosure added: encl=0