[plt-scheme] tcp-listen and Solaris 10 (sparc)

I am unable to use the tcp-listen function successfully using  
mzscheme 301 (downloaded binary) or 301.13 (built from source). The  
tcp-listen function always returns errno=125 even though the port  
number is available. I have tried a wide range of port numbers but  
the result is the same unless I try a restricted port number. Has  
anyone else experienced this problem? Pointers would be greatly  
appreciated.

Regards,
Jon

$ ./mzscheme
Welcome to MzScheme version 301.13, Copyright (c) 2004-2006 PLT  
Scheme Inc.
 > (tcp-listen 9000)
tcp-listen: listen on 9000 failed (Address already in use; errno=125)

=== context ===
repl-loop
read-eval-print-loop

 > (tcp-listen 80)
tcp-listen: listen on 80 failed (Permission denied; errno=13)

=== context ===
repl-loop
read-eval-print-loop

 > (exit)
$ uname -a
SunOS atldev0.informiam.com 5.10 Generic sun4u sparc SUNW,Ultra-60