File I created in After Effects 2024 and finished in AE Beta won't open in AE 2021

[Hannah389701810jac]

Hi there! I have a question about file compatability between different versions of After Effects. I'm currently taking a class in AE, and when I tried to open an assignment I did on a school computer (likely on one of the latest versions, probably a 2024 version) on my laptop (with AE 2021, version 18.0.0, build 39), I couldn't, getting this error message:

The file you are attempting to open was created with After Effects version 25.0×20 (Apple Arm 64) and cannot be opened with this version. See www.adobe.com/aftereffects for information on upgrading your software.

Additionally, early on in the assignment, when I opened it, it automatically opened up in After Effects Beta instead of After Effects like I'd originally made it in, and I've been working with the new, (converted) file since. Does anyone know whether this issue is caused by trying to open a new version (2024) file in an older version (2021), or trying to open a beta file in the non-beta version? I have an older laptop and anytime I want to update Adobe software, I have to contact their support and have them send me a direct download link, so I'd like to rule out the beta possibility before I do that. If I really do need to update, does anyone know to what version minimum to get it to work? Thank you.

TLDR; file I created in After Effects 2024 and finished in After Effects Beta won't open in After Effects 2021.

[Rick Gerard]

If you have a file created in 24, you have to open it in 24, then choose File/Save As/Save a Copy as 22x...

Then, you have to open the file in 23x or 22.x and repeat the process to save it as a 21.x file. 

It is also important to realize that features available in the latest version will be lost when you save the file as a previous version.