v3 to v4

having trouble opening some song files

i’ve recently gone to look at stuff i did in song files that i havent opened in a long time (2 or 3 years, in some cases) and found they wont open in 4.x. it’s not the case with my more recent song files, and not the case with all of my older ones.
the error message is pretty standard and non-descript. (running win2000SE)
i was wondering what some possible causes/solutions for this might be.
is there a link to ntrack 3.whatever somewhere. i dont recall having this problem before the upgrade… and then i could fiddle and see if it’s a vst thing, or… i dont know. help?

I had alot of problems opening my old song files, but it was because the track effects that were saved in the song file were not installed or used anymore. Do you still have all the effects installed ?.

i have the same stock of plugins, but if i used soemthign that came standard with 3.x and isn’t in 4.x… i dont know if there is one…