Can't re-write over an existing file.

That could be the issue, I'll look into it. Thanks for your help.

If your rendered file exists anywhere in the comp you are trying to render, or it is active in another program like Premiere Pro, you cannot overwrite it. I render different versions of a project all the time from different versions of the AEP file because I have had many clients want to roll back a couple of versions over the years. I also render and replace files all the time. I've never seen the process fail unless the file is in use somewhere in the project. BTW, resolve has the same limitations. If your rendered file is anywhere in the project it cannot be overwritten.

When you have an issue that didn't exist for all users that mean you have something wrong to be not able to re-write over an existing file mostly it's an OS issue, so double check if you have any permission for your file also check if you give the adobe software full access to your HD from the security settings.

When you post a question you always need to tell the Adobe program you are using
There are MANY programs in a full subscription, plus other non-subscription programs
Please post the exact name of the Adobe program you use so a Moderator may move this message to that forum