CakeAlexS
When opening the Project in Sonar X3 and saving it you converted it to a X3 project, doesn't matter what you did.
8.5 cannot open X3 projects (not backward compatible)... as far as I know???
Revert to a backup assuming you took one, otherwise you are going to have to get into messy exporting.
 
Any real reason why are you reverting to 8.5?
 
Cheers..

Sonar is backward compatible. New versions can and do open older projects created in older versions. Older versions are not forward compatible.  That is, an older version is not guaranteed to open a project created in a newer version. 
 
To the OP really all he needs is Sonar X3 which is $49.00 to upgrade. Surely that wont break the bank.  

John
 
To the OP really all he needs is Sonar X3 which is $49.00 to upgrade. Surely that wont break the bank.  

It was less than $20 a few weeks ago.

CakeAlexS
When opening the Project in Sonar X3 and saving it you converted it to a X3 project, doesn't matter what you did.
8.5 cannot open X3 projects (not backward compatible)... as far as I know???
Revert to a backup assuming you took one, otherwise you are going to have to get into messy exporting.
 
Any real reason why are you reverting to 8.5?
 
Cheers..

 

John
Older versions are not forward compatible.  
Sonar is backward compatible. New versions can and do open older projects created in older versions. Older versions are not forward compatible.  That is, an older version is not guaranteed to open a project created in a newer version. 
 
To the OP really all he needs is Sonar X3 which is $49.00 to upgrade. Surely that wont break the bank.  

Sorry I meant to say Sonar 8.5 is NOT forwards compatible.... well I say that, check here .
 

I know Alex. I just didn't want the OP to get confused. We all make typos. 

John

CakeAlexS
When opening the Project in Sonar X3 and saving it you converted it to a X3 project, doesn't matter what you did.
8.5 cannot open X3 projects (not backward compatible)... as far as I know???
Revert to a backup assuming you took one, otherwise you are going to have to get into messy exporting.
 
Any real reason why are you reverting to 8.5?
 
Cheers..

Sonar is backward compatible. New versions can and do open older projects created in older versions. Older versions are not forward compatible.  That is, an older version is not guaranteed to open a project created in a newer version. 
 
To the OP really all he needs is Sonar X3 which is $49.00 to upgrade. Surely that wont break the bank.  

Older versions should be capable of opening newer projects. The link Alex supplied specifically states that V1 & V2 cannot open X3 projects and as far back as V4 is dependent on 64-bit data.
 
There is no guarantee though. The fact the OP can open it in 8'5 on his system yet his colleague can't on a different system suggests to me that there is something more than new project/old version going on here.

Note....... that's V1 & V2 NOT X1 & X2
 

Collaborator has multiple (paying) clients.  I'm a freebie friend.  He's unwilling to change his system mid-stream.  I understand that.  He cannot afford to purchase a new PC, but that would be the ideal solution to me.
 
I will install the 32 bit version of X3 and try saving the projects and resend them to him.  We're using an external HD to transfer files since our album is almost 64Gb of raw wave so far.  I love the fact that both versions have no trouble handling the 120 + tracks we have going on some of these epic pieces!
 
Again, thanks to all of you for the insightful responses.  (And the $20 upgrade is a no-brainer as far as I'm concerned!)  I only wish I could afford to buy him a new PC...  Then he could upgrade, but keep his 8.5 system.

John
I know Alex. I just didn't want the OP to get confused. We all make typos. 

I understood and quite right! Might have been confusing myself :)

Rodan
Collaborator has multiple (paying) clients.  I'm a freebie friend. 

A freebie friend that's now gonna charge him $20 for a free Sonar upgrade .
 
Cheers...

Rodan
8.5 generates a message warning that the project has been edited with a newer version of Sonar.  The dialog box has the helpful "OK" button.  Pressing "OK" (as that is the only option) causes the hang.
 
I tested opening the project on my laptop - which still has 8.5 on it and for me, the dialog is followed by successful opening of the project.  My laptop is W7/64 Home.  My DAW is W7/64 Enterprise.  My collaborator is running W7/32 Pro.  My assumption is that the OS difference is causing the problem.  I just can't find a way to "save-as" the CWP to default to 32bit OS on my X3 Sonar instance.
 
Thanks all for the questions and helpful replies!
Dan
 

So if you can open it in your 8.5.... Save it in 8.5 and send it to your friend.