SCO Error code 28

With SCO OpenServer Enterprise 5.0.4 installed in IBM Netfinity server, it has been hang for few times. nothing display on the screen (blank screen).
After rebooting, the following messages display:
fsstat:/dev/u needs checking
mount:possible damage file system, mount failed
No space left on device (error 28)
/dev/u
HTFS file system : Volume
No partial Transaction pending
File system state set to OK
10360 files 2202075 blocks 2751446 free
***file system was modified***
mounted /u file system

Appreciated for advise.