Hi there
I just had the same behavior today when I installed ARCserve 2000 on a Windows 2000 Advanced Server machine where a few dozen users where sitting on (was a fileserver). Just right after I installed the Backup Agent Open Files, most of the users got instantly disconnected and new users trying to connect to their shares on this servers could not connect (so I was in a bad, bad situation).
I took a short look into the system event log and found a huge amount of the same message saying something like: "the value for the parameter "irpstacksize" is set to low to serve a local device".
Well I had just a similar problem with installing CA SurviveIT 2000 on two Windows NT servers and also InoculateIT 6.0 Workgroup Edition on a Windows NT server (no connections possible any more). So today I tried the same thing as I did in the past with my SurviveIT and InoculateIT problem experience:
- start the regedt32 program
- switch to the window HKEY_LOCAL_MACHINE
- open SYSTEM / CurrentControlSet / Services / LANManserver
- select the "Parameter" key on the left side and take a look at the values on the right pane side
- you most likely will find a value "IRPstackSize" with a value of 13 (decimal) or any other value
- Rename (or delete and redefine) the Key to the correct syntax "IRPStackSize" (Capital letter for the beginning of "Stack"

- Set a value of say 24 (my guess-value on todays installation)
- Close regedt32
- Stop the service "Server" (this will automatically stop "Distributed File System", "Computer Browser" and "ARCserve Discovery Service" as well other possible, depending services.
- Restart the service "Server" (I think this will autostart the "Computer Browser", but you still have to start "Distributed File System" and "ARCserve Discovery Service" manually.
- tell the users to try to connect to the server again
- everything should be "normal" again
I think, some of CA's setup routines are putting the "IRPStackSize" into the LANManserver parameters list. I think of this, because before installing CA software this key does not exist yet in the parameter list. I read in MS Knowledgebase that the default value of this key would be 11 (although not visible in the registry, the key exists in the "background" and has a value set to 11). You must define this key manually and assign the value, to override the default value (11). Why CA's setup is defining this key and is setting it to 6 in SurviveIT 2000, or 4 in InoculateIT Workgroup Edition - I really have no clue about. I just know, that no other setup program I know is doing this to me ... And: CA's setup is not doing this always (just to confuse totally).
So remember to check the IRPStackSize key in the registry whenever again should installing any CA software disconnect your users / applications from the server you are installing the software to.
Please give me a feedback, if this workaround helped. Sorry for the long text, but I like to hit my keyboard (softkeys - hehe).
Kindest regards
david a. marton, restorage gmbh - switzerland