U61 requires ClanLib to run.

ClanLib is a game programming library, and you can get it at:
http://clanlib.org

U61 has been reported to work with ClanLib 0.4.4

If you have successfully installed ClanLib but still get an error
message, please check that you have done at least one of the
following (supposing that you installed ClanLib in /usr/local/) :
- add /usr/local/lib to your /etc/ld.so.conf file
- run ldconfig in /usr/local/lib

Also check that you have the clanMikMod and clanLua modules.
You'll need to get libMikMod and Lua before you can use those BTW.

If it still doesn't work, send me a mail at:
ufoot@ufoot.org

Good luck!
