rsync - Jul 2008 - maximum block-size (-B) parameter

I've been trying to test rsync on files over 80GB again to see if I can find
ways to improve performance further.  I tried passing a manual block-size
value and I keep getting "Invalid block length" from the [sender]. 
Can
someone refresh my memory of the valid values that can be passed using this
parameter?  

I've tried passing 1048 and the -vvv output shows the file being processed
in 1KB intervals.  I pass 1048576 and I get the error message from the
sender.  I have not modified the define in rsync.h, it is still ((int32)1
<<
17).  Since the value is an int32, passing 16MB or 1MB or 512KB should not
be a problem, right?

Rob

The maximum value allowed was 128KB.  I think this is an issue with cygwin
(using 1.7.6 for testing) and how it interprets an int32.  I've modified the
define value from the int32 and put in an upper limit instead to test.  Just
an FYI in case someone else has this issue.

Rob