Cadence Virtuoso: Unable to write changes in memory to disk for file

I have been working on a layout in virtuoso and after copying my cellview in a new cellview, I could not anymore save changes in the old and new cellview. As I start virtuoso, I have several warnings messages even before opening my layout. The messages are of the type below:

*WARNING* envSetVal: Can't set the value of variable 'weTapWidthOnPins',
\w in tool[.partition] 'layout' - it has not been registered.
\w *WARNING* envSetVal: Can't set the value of variable 'drdEditFilterLayers',
\w in tool[.partition] 'layout' - it has not been registered.
\w *WARNING* envCyclicStringToIndex: could not find variable 'snapPatternDrawingStyle'

I am running virtuoso version 6.1.5-64b on CentOS. I can open the schematic and the layer but when I try to save the layout, I have the message:
*WARNING* (DB-270000): dbSave: Unable to write changes in memory to disk for file '/afs/ee.up.ac.za/user/a/abimana/new_ibm_dirV2/phd_work/layout.oa.cadence3.ee.up.ac.za.24160.20150906200000.tmp.a'. OS error code: '5': "Input/output error"
\w *WARNING* Cellview phd_work LNA_April26_nofloat_real layout could not be saved.

Can someone provide indications on the cause of the error and possibly directions for a solution?

Best Regards, Aba