Using tar with block size 1024

[Budiono]

Hi all,

When I backup my harddisk using tar script into tape backup, using 
block-size 1024 and Redhat 9.0 system it running well. But in my new 
system (Fedora Core 6),using tar for backup with big block size (1024) 
it get error message:

[root at mis-s155 ~]# tar -b 1024 -cvf /dev/st0 /usr/local/src
tar: Removing leading `/' from member names
tar: /dev/st0: Cannot write: Device or resource busy
tar: Error is not recoverable: exiting now

But it run ok but slow when using block size 128, higher than that, it 
get same error as above message.
I looking in google but get no satisfy solution, some link in google I 
found that module st.o have some problem in kernel 2.6 ?

Does any one have the same experience ?

Thank's
Budiono