Firmware 1.9.2.7-d-r655

For some reason - just recently - when trying to vi any file I am getting the "not a regular file" error and no file content is being displayed. Using the cat command displays the file ok. I suspect there is a problem with mounting, df command displays:

[admin@ASS root]$ df
Filesystem Size Used Avail Use% Mounted on
rootfs 2.9M 2.9M 0 100% /
/dev/root 2.9M 2.9M 0 100% /
tmpfs 15M 208K 15M 2% /tmp
/dev/discs/disc0/part2
966M 101M 816M 11% /opt
/dev/discs/disc0/part3
228G 41G 176G 19% /tmp/mnt/disc0_3
[admin@ASS root]$

Can anybody help to resolve it? Thanks Adam