Odds are that this is related to your antivirus program. There are many threads on this forum where posters have encountered similar errors due to their overactive AV. For example, see the one below. Try a test by disabling your AV and see if the problem is corrected. If so, whitelist Scrivener.
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To create new posts, you actually need to be in a specific board. My guess is you were looking at a board index or Active Topics or a board search, or some other place that’s not in a specific board.
To create a new post in the Technical Support (Windows) board, do this:
Go to the board index: https://www.literatureandlatte.com/forum/index.php
Find the link that reads “Technical Support (Windows)”. It’s under Scrivener > Scrivener for Windows. Click on the link. You are now in the Technical Support (Windows) board.
To create a new post, click on the big red New Topic button.
Best,
Jim