thanks for all the replies. Here is also, what I received from support.
Very sorry for the late reply to your request - our help desk has had some issues over the past few days.
Since none of the troubleshooting steps have worked, I'd recommend doing the following exactly.
Step 1 - create a new project file
Step 2 - copy/drag each page (1 by 1) to the new project
Step 3 - save after adding each pageIf you are able to move all pages over successfully, then perfect.
Your file may have been corrupted when moving it. If not, then the page you added last before trying to save is the cause of the issue.
We can then narrow it down to a plugin / code, etc.
Support @ Realmac Software
When the problem manifested itself, I was using version 7.3.3 and I am only using the plugins, that come with RW, no updates. Part of the problem was, that I could no longer save any file, no old ones and no new ones. So the steps mentioned above would not have worked. Also, I did not move the file, so moving it should not have been the cause of any corruption. Between the file working and the file no longer being able to be saved, I corrected some spelling errors. The plugin that seems to be affected is the "Styled Text". Where there is usually a "A" symbol in the sidebar, there is now only a "lego" like symbol. I will send support the project file.
I have since downgraded to version 7.3.1 in which I can no longer open the file that was affected first, but I can open other projects and also create new ones. As to the project I was working on at the time, I had to completely recreate it from scratch and am still working on that.
While downgrading and rebuilding the project gets me working again, it does not solve the software issue at the heart of the problem. I would still like to get that resolved.
Thanks a lot!