I've just loaded 1.7.1 over 1.7 (and the additional components) and get loads of XML errors when I start the program. Below is just one file and its error message.
BlueBrick had encountered problems while loading XML files from the parts database. These XML files have been ignored. This problem may happen if an XML file contains syntax errors. Fix the syntax or delete the XML files to remove this warning. The file(s) concerned is/are:
Invalid character in the given encoding. Line 6, position 8.
Looking at the XML I think the problem is the accented characters in the French desccriptions.
In the 1.7.1, the encoding format of the part XML files has changed for compatibility reasons with Mac and Linux.
Now the part XML files should be encoded in UTF-8. Therefore I advise you to:
1) Unzip the 1.7.1 on a clean folder to avoid some old files in ASCII that have been renamed.
2) Download again the additionnal packages if you want them, and unzip them in the 1.7.1 part folder.
3) Copy your custom parts in the 1.7.1 part folder then convert the encoding to UTF-8 (with your favorite text editor) and add the encoding in the first line of the XML file (you can look into a 1.7.1 part as an example).
Sorry for the inconvenience.