MK IV navigation issue

I have a 330 ci of 2003 with a 16:9 navigation screen and a MKIV module in the trunk. It was delivered with a v21 software and a dvd Europe High 2003 for the maps. Last year I have downloaded from the internet (yes, stupid me !) v31 from a Portuguese guy. By the way, I live in Portugal. I then burned the CD and inserted it and the download was successful, i.e. I got all the screens and messages I had to see. Everything works fine ... in Portugal. Once I get to the border in Spain, the screen turns black, re-starts twice or 3 times and then freezes. When I restart the engine, the gps immediately recognizes my location in Spain, France, Belgium and I can program and use the gps ... for only 1 or 2 minutes and then the screen freezes again. I went last week to a BMW garage in Belgium and they downloaded V32 but the same problem remains: I still get the splash screen of V31 and after 1 or 2 minutes the screen goes in freeze mode (but not in Portugal). So, I went to a BMW garage in Portugal and they do not know what to say: it seems that it is impossible to erase everything from the system and start again from scratch as all data are written over and over and over when upgrading to more recent software versions. At the garage, they are not even sure that a new dvd reader is the solution as a dvd reader is supposed to read only the data stored somewhere else than in a reader device. So my question is as follows: where is the data stored and can I purchase that device separately instead of buying a 1800 Euro new MKIV system, which is stupid because the most recent Tom-Tom Go 950 costs only 300 Euros. Please help as I would prefer to use my current MKIV with a minimum of costs. Thank you in advance. I will never download from the web again ...