Is there a file called sdata.grf in your RO folder? Make sure it's there, it should be included in the full setup, and its size should be around 1.2 GB. Also, make sure the file called "data.ini" or simply "data" contains the following lines (double click on it to see its content in notepad):
[data]
0=abdata.grf
1=rdata.grf
2=sdata.grf