That error message could be generated by one of these three issues:
1. The savegame file (i.e. RVFOREST.DAT) is not stored in the location stated in the dlcsetting.xml file (therefore, the application fails to open such a file and should terminate)
2. The size of savegame file is bigger or smaller than it should be (therefore, the application stops the process to make sure it is not a corrupted one or it could be some other file but somehow has the same name and location as defined in the dlcsetting.xml file)
3. The application cannot create temporary file (e.g. TEMP.DAT) as defined in the dlcsetting.xml file
I would think there is more probability that it is the first one. Check your dlcsetting.xml content. Since DiiLC v1.2 creates a new dlcsetting.xml (with version number = 2), then you may need to edit it again to get the right location where you store the RVFOREST.DAT file.
Let me know if this does not solve your problem..