I have found that you can fix this problem by opening the mods.cfg that is located in the same folder as "Flax's Arma Server Tool.exe" use notepad++ or something similar.
the file contents will look something like this:
333310405,Enhanced Movement,5/3/2018 10:01:22 PM,8/6/2017 3:47:17 PM,public
1128256978,Chernarus Redux,5/3/2018 10:04:09 PM,3/20/2018 9:48:55 PM,public
1113351114,DS Houses,12/11/2017 7:05:11 PM,12/8/2017 6:11:19 PM,public
501966277,Zombies and Demons,11/29/2017 11:10:41 PM,5/28/2017 5:12:04 PM,public
807038742,Project Infinite - All in one,2/20/2018 7:51:37 AM,2/14/2018 6:11:34 PM,public
you need to as a , in front of public
in notepad++ click find and replace.
find: ,public
replace: ,,public
click replace all
save.
should look like:
333310405,Enhanced Movement,5/3/2018 10:01:22 PM,8/6/2017 3:47:17 PM,,public
1128256978,Chernarus Redux,5/3/2018 10:04:09 PM,3/20/2018 9:48:55 PM,,public
1113351114,DS Houses,12/11/2017 7:05:11 PM,12/8/2017 6:11:19 PM,,public
501966277,Zombies and Demons,11/29/2017 11:10:41 PM,5/28/2017 5:12:04 PM,,public
807038742,Project Infinite - All in one,2/20/2018 7:51:37 AM,2/14/2018 6:11:34 PM,,public
FAST should now work. you can open and close it and re-open it.