There are some reasons why that kind of error appeared:
1. Your client exe is reading the wrong set of lua/lub files. To fix it, svn checkout this: http://svn6.assembla.com/svn/ClientSide/Lua_Project/ then update your grf with those files you have downloaded.
2. Check if your data.ini is in the correct format. Usually, if you are using a custom grf, you need to write it this way:
[Data]
0=your.grf
1=data.grf
2=rdata.grf
3. Check as well if you have diffed your client exe properly. If you are using ShinsDIffPatcher, then you should just use the recommended diffs.