You would really need to include more information to your setup. RunUO version used, client patch version used, and what you have done to configure everything up to this point - as in, ServerList.cs edits, DataPath.cs edits and anything else related to your setup to this point.
If you are using a standard distro RunUO 2.3 and a client at or over 7.0.24, you may have the typicall issue with RunUO not having the support for the new EA games *.UOP file format, and will cause you to fall through floors and some map tiles.
If you do not have RunUO using the same map files that your UO client is using, you would get these results too.