@Dimitri
The "Object reference not set to an instance of an object" is almost always an error in the xml file. Last file to be loaded is the MercStartingGear.xml so you'll have to either check it yourself to find what is wrong, or upload it somewhere and let us take a look at it. Best to upload the whole tabledata folder, so if there are any other files with problems, we can find them. I may be able to take a look at it tomorrow, but not sure I'll have the time.
The error is almost always the inclusion of an item id that doesn't exist in the items.xml, though it might be possible to encounter the same thing with a merc id that doesn't exist, though I think that is much more difficult to accomplish.