You are spot on....I did create the file on a Windows PC, so I did what you suggested and I got the file to execute. Thank you for that.

I found I had to change some of the paths in the file location section of dyndns.sh (/devbin instead of /hack/bin).
Now I get to the part where it's supposed to get my IP address and it falls over.
[TiVo [p0] /var/hack]# /var/hack/dyndns.sh
--13:34:44-- http://www.myipaddress.com/
=> `index.html'
Resolving www.myipaddress.com... failed: Host not found.
grep: index.html: No such file or directory
rm: indexhtml: No such file or directory
/bin/cat: /tmp/ip.txt: No such file or directory

I don't believe the router (Netcomm NB1300PLUS4) is a problem as the Tivo makes the daily call OK.

Any thoughts?