wouldn't it be awesome if Cakewalk invented a utility for opening up corrupted .bun & .cwb files?  i have so many old projects that i have no access to anymore because, stupidly/ignorantly, saved them as .bun or .cwb.
trying to open them in "safe mode" doesn't count, because then they open up as if nothing were ever there i.e. no audio or midi.  i mean if there is only one detail that is corrupting the bundle, then make it so the bundle will open up completely, but with the exception of that one debilitating item.

I opened a couple of old bun files last month and other than some problems with plugins I don't use anymore they opened fine.  These were about 11 years old made in home studio for the first album I ever recorded.
 

back up is your friend. :-)

yes. backup is my friend now, but way back then i was flying blind and stupid and all i have are these unopenable .bun & .cwb files to prove that unfortunate fact

i mean if there is only one detail that is corrupting the bundle, then make it so the bundle will open up completely, but with the exception of that one debilitating item.

This is called CWP and per project audio files. This had been around since CWB/bun files. These are less likely to get corrupted and they will open if they ever do. 
 
CJ

Is it possible that it may be opened on another computer rig?  Sometimes a particular computer may not be able to open the file while another one can...

i DO use CWP and per-project audio files, and have since Sonar 7 when i first learned about my corrupted bundles.  so i am talking about stuff from years ago.  not now.  

CWP have been around for years. Just as long as CWB had been around

I think the OP is acknowledging the mistakes made from the past, and is just wondering if there were any way to get at some of the older projects that no longer seem to open.
 
Bob Bone
 

I don't know how many different versions of Sonar you currently have installed but I would try opening (copies of) the bundles in all of your different versions - it may make no difference but if even one opens you've at least saved that one.