Sounds like something is wonky with your third entry file. Here are some things to try:
Verify that you have a file 00000003.cgi in your archives directory (that is the file gm needs to create the html files (or whatever your preferences are set to).
Run Diagnostics and Repair and make sure that works. Check your gm-entrylist and see the third line, it should contain summary data of your third entry. Then try to rebuild all files.
Make a backup of 00000003.cgi (rename it to 00000003.bak) then copy your entry 00000002.cgi over it (rename 2 to 00000003.cgi). Do a Diag and Repair, then a rebuild all.
Look at the file 00000003.bak and get your inital main and extended text out of it (it will be the 3rd and 4th lines of the file). Replace every instance of |*| with a newline (return). Edit that new 3rd entry in GM and put your text back in. You can then directly edit the file (with a text editor like pico or vi), to fix the dates and what not.
You will loose the comments on that entry, unless you copy everything after the 5th line (including the 5th) and put it directly in the file 00000003.cgi (starting with the 5th line).