I hardly have the need to open any Sonar projects in versions previous to Platinum. But today I was just curious to check backward compatibility. I randomly tried to open into X3e Producer some of my recent projects done in Platinum.
 
I can understand the below message while opening some of them (the project opens when I click "ok") :
 

 
 
But I can't understand why I get this below message while opening some (the project doesn't open at all) :
 

 
 
Why would a project not open at all stating incompatibility ? I thought it should open with the more recent features not being available, that's all, shouldn't that be the case ?
 
 

I cant really read the message as the windows error message box in very small.
I have been able to open projects in platinum that I have created in X1 (as little as last month)
I haven't however tried this since updating to 9.2016.
 
Try opening the project in Safe mode.
Hold SHIFT while opening Sonar.

There are very rare cases where we intentionally marked projects as incompatible to earlier versions. The only time recently when we had to break compatibility intentionally was for Patch Points. This is documented here. There is a simple workaround should you need to open it in an earlier version. 
Patch points use a drastically different routing that earlier versions cannot understand so we have to block them from loading.
In Platinum we actually have a nice error message that tells you what feature specifically isn't compatible. Unfortunately X3 doesn't know how to tell you that.

Noel Borthwick [Cakewalk]
There are very rare cases where we intentionally marked projects as incompatible to earlier versions. The only time recently when we had to break compatibility intentionally was for Patch Points. This is documented here. There is a simple workaround should you need to open it in an earlier version. 
Patch points use a drastically different routing that earlier versions cannot understand so we have to block them from loading.
In Platinum we actually have a nice error message that tells you what feature specifically isn't compatible. Unfortunately X3 doesn't know how to tell you that.

Noel, thanks a lot for your quick response on this one. I guess that pretty much explains it. I checked back after your post and realized that my projects not opening in X3e did have aux track and patch point routings. I was wondering if there was any way for projects to automatically re-assign such routings to "none" or any other compatible ins or outs when opened in older versions. Somewhat like how MIDI routings are re-assigned to certain defaults if a certain midi controller with which a project was saved happens to be disconnected when opening the project.
 
Creating a copy project file is the easy part. But things could get cumbersome if there are tons of aux and patch point routings. Well, another way could be if a command button is introduced, say somewhere on the control bar, on clicking of which all aux and patch point routings will be reassigned to some default in a stroke before saving the file for opening in older versions. Just thinking aloud sort of... 
 
 

That is like asking a prior version to predict the future :) How would X3 have dreamed that there would be a feature called patch points? 
You could probably use quick grouping to reassign any outs to patch points relatively easily. Or just delete all aux tracks which should automatically do it I think.