Studio 2015: error adding bookmark

Hello,

Attempting to bookmark a segment in a Studio project, I get this familiar error message:

"Attempted to read or write protected memory. This is often an indication that other memory is corrupt."

I have already added several bookmarks ( managing to lose them as well!) in this project.

Now it won't let me add any more - the basic translation process seems t be proceeding OK.

The whole bookmarks feature seems a bit flaky - a message also comes asking about bookmarks in projects removed from the list, when I know there aren't any.

I have also enabled the return to the last position in the active file, this doesn't work very well either - it activates the right segment (visible in the Translation results window) but the display does not move!

Anyone else seen this?