When I try to update the package list in luci I get the following error message;

    Error (Code 255)

Any ideas on what could be the problem?

It is under investigation. Opkg was updated recently and some command line parameters changed.

The only time I get that error is if A) DNS resolution is not configured properly on the router or B) your routing is not set up so that it can get to the internet (or firewall is blocking). My guess is that it's a DNS resolution problem. Can you "ping www.google.com" while logged into the router command line?

EDIT: Actually I get Error (Code 256) when it cannot resolve IPs or doesn't have a route to the Internet or is blocked. I see your code is 255, you can likely forget what I said.

Any chance to clean-up this for 10.03.1 release?
I get error code 255 with 10.03.1-RC3:

Install 'collectd-mod-rrdtool': Error (Code 255)

Q: Is it possible to understand memory (flash) requirements for package to be installed in OpenWrt?
I have router with 4MB flash, an dit can be that it just doesn't have enough memory to fit that package.

I have installed before this:
# opkg list-installed | grep collectd
collectd - 4.9.1-3
collectd-mod-cpu - 4.9.1-3
collectd-mod-interface - 4.9.1-3
collectd-mod-network - 4.9.1-3

Router now shows : Free space: 23% (120.00 KB)
So all available space was about 450KB.
Just wondering how to fit Network Traffic and Wireless Sattus charts into this memory, and get it working.