Got a new Poser 12, and lots of Poser 11 files. When I open a poser 11 file, three things may happen:

1 I get an error message that says "this file was created by a previous version of Poser. Poser will attempt to import it". sometimes it can open the file after  a few minutes thinking, or may just crash.

2 immediately crash, no warning message. As soon as I click on the file to open it, a spinning colorful ball appears and poser is totally paralyzed.

3 the 11's file opens as usual, like any other poser file. I can male any change I like, save the file, and next time I open it, it is perfectly normal.

Any idea why some files open as usual, and why others cause poser to crash?, but more important, how can I solve this? (I've got tons of older poser 11 files).

I've seen some old, poser11-generated scenes loading and rapidly crashing poser12, have you tried to import one of those old scenes, instead of opening it directly?
If it works, save it immediately under a new name.

Sometime, deleting unwanted items from a poser11 file in poser12 can crash it, especially if there is some parenting plus not visible objects.

Ty Phil. I followed your suggestions, but unfortunately nothing changes. I even made copies, exported the problematic file, saves as, etc, but no. For some reason, the files that cannot be opened with poser 12, crash immediately.
The bright side, I can still use Poser 11 to work with those.

To get everything pushed towards poser12, it can become a tedious task, but that's doable.
For example, each character (with its clothes/equipment/whatever) can be exported of poser11 using File > export > partial scene  and then reimported in poser12 using the "import poser document" function.
And don't forget that as long as you aren't rendering using both poser's at the same time (except under some specific conditions), both can run in parallel, so that you don't have to close one, reopen the other, reload stuff, and so one.

This is a way, another is to store in a dedicated runtime structure each item separately. But this is a long term solution, and it is for another use.

In the case of Windows, and if your system drive has enough space, your PC can handle both at the same time, even if it may take some time because of memory swapping, depending on the RAM your computed has. It' not that difficult, as poser is rather good at this: I have an external scene with a swimming pool, a 2k hdri and 13 victoria4's each with its 3 4k diffuse maps + 3 bump maps, and poser12 needs less than 5Gb of RAM, as long as I don't launch the render (it then can jump up to 18Gb...)

To get everything pushed towards poser12, it can become a tedious task, but that's doable.

Thanks for your suggestions Y-Phil. I tried them all, and some other suggested by Poser's support team. This problem has been solved, thank you. There's a couple of hidden folders named F6C5GMLRY9.poser, and  Poser.savedState. Once I trashed the first folder complete, and the contents of the second, Poser was able to open any file with no problem at all. This solution has already added to Poser's Knowledge Base

chombeaux posted at 11:58 PM Mon, 13 March 2023 - #4458378

Y-Phil posted at 6:21 AM Sun, 12 March 2023 - #4458201

To get everything pushed towards poser12, it can become a tedious task, but that's doable.

Thanks for your suggestions Y-Phil. I tried them all, and some other suggested by Poser's support team. This problem has been solved, thank you. There's a couple of hidden folders named F6C5GMLRY9.poser, and  Poser.savedState. Once I trashed the first folder complete, and the contents of the second, Poser was able to open any file with no problem at all. This solution has already added to Poser's Knowledge Base