Watchdog Problem In Unix Server

My Unix Server with SCO Unix ver 5, display Watchdog error which reads,
Watchdog ReInitMemory 6 for board 0 Warning : eeE : Allocb failure in ReInitMemory.

My server has 98 dumb terminals connected. It has 5 Hard Disks (SCSI) of 9.1 GB each and 512 MB RAM. Uses RAID level 5
After this error all the dumb terminals hang, but I am able to give shutdown from console using root login. After restart We all can work.

What is Watchdog Software ? What are the causes for the error and how to rectify ?

Some times the console shows the following warning on the screen
Table-grow - No Memory available for edblock table

What is edblock table and what does it contain. What cleanup action should I take to create space in the table ?

As far as edblock table error, read the answer towards the bottom of the link - you may not have enough physical memory to run the amount of connections or not enough memory allocated for the amount of connections. More than likely your watchdog errors are either from this problem or you may have some bad memory.