Will need more information:

1. How are you running windows AutoCAD LT 2025 on your Mac?

2. What kind of network is installed?

3. If you don’t save over the network but just locally on your Mac does this work?

4. When you run other software on your Mac are you able to save that file over the network?

@infoT7QWV What does "file becomes unrecognisable" mean to the rest of us way over here?

For example, where and how does that error appear, how do we all try to repeat what you see?

Is this just you or everyone accessing the Windows Server folder in your office see this error (and in what form does it appear, and how)?

So far, from your light post, you have an I.T. issue, nothing more, we can't help you with local I.T. issues.