Question: Why does Web2Disk change the filenames for some of the URLs it downloads? It seems to be adding a random set of letters after the filename (but before the extension).

Answer: This behavior is normal. Web2Disk automatically renames the URLs that have parameters to make the file names compatible with Windows. 

For example, if Web2Disk were saving this URL:

http://www.inspyder.com/support/KnowledgeBase/Article.aspx?Article=213
It would rename the "Article.aspx?Article=213" part to "Article_xxxxxx.aspx.htm" because Windows does not allow you to have a file name with "?" in it. This also serves to shorten long file names (Windows is limited to 255 character file names).

After Web2Disk is finished downloading all the pages on the website it will automatically fix the links so that you can browse the new filenames while offline.

If you want to disable the renaming, turn off "Rename Files and Dynamic URLs" in Advanced Project Settings. Note that if you disable this, some files will not be able to be saved (because they contain characters that Windows does not allow).