In the contrib directory, the cvsdiff script is nominally a #!/bin/sh script, but contains a bash-specific line and so will fail on systems on which /bin/sh is not bash.
This was reported in Debian:
http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=489666
The one line patch is given on that bug report page. We've already applied it to the Debian release of tkcvs.
Regards,
Tim
Fixed in version 8.2