Hello! Sorry about the inconvenience, hopefully we can get to the bottom of this.
First of all, have you tried relogging and then /setforsale again? Sometimes relogging can work some magic and who knows.
If you have and it did not work, I would firstly fill out a bug report. Then I would find an admin or a trustworthy friend in game, /sell <id> <VID> <1> and see if that allows you to sell it that way. Then buy it back from the person and see if it will let you /setforsale.
Once you've tried that, post a reply here and see where we are. Good Luck and sorry about the bug.
Like cradboard said, relogging should fix the issue. Some players have experienced this issue as well, and relogging did the trick.
Since you haven't visited the forum for five days, and no response was given by the OP, I'm going to make this query as inactive. If you have any other concerns, please feel free to make another thread in the Help Section.