This can be caused by various problems, or just by the fact that I am not very good at writing help files (you have read the help file, haven't you ?). Try the following :
This is a problem with the drivers for certain high performance video cards. The driver for the card does not properly handle patterned flood-fills. If you go to the Map-Colours option on the Options menu in Mapper, and set both land and sea to 0, then the problem will go away. You will not get shaded sea either, but that has to be better than a system crash.
Version 1.17 and Version 1.2 are identical, except for the version number. I just forgot to update the number before releasing it to the world.
This was a problem with the original set of files for the Colonial Variant. The problem has now been fixed. If you go back to the Mapper home page, and download the latest version of colonial.zip, and unzip it into your Mapper directory, over the Colonial files you have there already, then the problem should be solved.
This is an error in the file variants.lst. It gives the variant name as Fleet_rome when it should be Fleet_Rome (Note the capital R). To fix it, load variants.lst into Notepad, or a similar text editor, and find the line Variant:Fleet_rome. Change the r to an R and save the file, and it should work fine.