There are a 2 things to try if you are seeing the "Cannot set block size to 
131072. Maximum transfer size supported by this system is 65536" errors.

1. Change the Win2003 SP1 tape.sys back to the tape.sys from Win2003 SP0. 
Change it in dllcache first (and press "replace anyway" when Windows warns 
this is a mismatched version for SP1), then also overwrite the copy in 
System32 after that. Microsoft seem to have hard-coded this problem in tape-
sys 2 years ago and not bothered to fix it since.

or

2. run    mt -f \\.\Tape3 status   to see the block size. Although this 
drive is in a library, it is attached to your system (i.e. \\.\Tape3). It 
should have something in the registry relating to it's attachment to your 
system, so identify the device location in the registry that it is attached 
on (in my case that is an Adaptec AHA-2930CU PCI SCSI Controller. It's 
Device Driver is located in the registry at :

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\aic78xx

For your device, once you've located it's key, go to the Parameters -> 
Device subkey. In my case, I have to create both Parameters and Devices, so 
that I have the path

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\aic78xx\Parameters\Devi
ce

Then, in Device, create a New DWORD and call it MaximumSGList

You can either simply set the Maximum to hex ff to allow any situation or 
set it as follows :

hex 11 (decimal 17) for 64kb block size
hex 21 (decimal 33) for 256kb block size
hex 41 (decimal 65) for 256kb block size
hex 81 (decimal 129) for 512kb block size

MaximumSGList = (Maximum Block Size)/4K +1

i.e for the size requested by NetWorker (131072 bytes) you need
131072 / (4*1024) + 1 = 33 decimal = 21 hex -> 256 kb block size.

Reboot the server.
Check the block size with   mt -f \\.\Tape3 status

In there you should see the following 2 lines

default blocksize = 65536
maximum blocksize = 131072

Those errors should no longer happen.

Regards,

Roy.

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