Hi -
The Exchange errors could be a result of your log files being full. You probably need to change your log settings. Go to Computer Management, either by right-clicking My Computer and select Manage Computers or by opening the MMC and selecting this add-in. Drill down to System Tools - Event Viewer. Right-click Application event log and select Properties. On the General Tab it should say "Overwrite events as needed." The size of my server log files are 8192 KB. You should Save the log file to another drive on the Unity server, not the C drive and then clear it. Do the same for all other logs.
Do you have Exchange performance analyzer running on this server? If so, it could be producing the errors because your disk performance counters are disabled, check out this link - http://technet.microsoft.com/en-us/library/aa998009.aspx
Ginger