when i try and do f1 command it says that stacksizecontroller has encountered an error while trying to read data file. 

Have you tried deleting the data/config file and regenerating it?

Always get the following error, no matter which command I enter:

StackSizeController has encountered an error while trying to read the data file. Please contact your server administrator to fix the issue.

How can I fix it?

Literally what it says, fix your errors in your data file..

i also have this issue but have done a clean reinstall over half a dozen times

hey, i have this to, thing is i can't even find a data file called stacksizecontroller or anything like it, i do have a config file and i've done multiple clean installs but to no avail

I have completely rebuilt the server. Then I just installed StackSizeController and it worked. Now I installed more plugins and now the same error again. Is this due to another plugin?

what plugins do you have? these are mine
AdminHammer
AdminMenu
AutoBroadcast
Autolock
Betterchat
Betterchat Filter
betterchat Flood
BetterLoot
Clans
ClansUI
Clearnight
CraftQueuSaver
DeathNotes
EnhancedHammer
ExplosionTracker
GatherManager
GUIannouncements
HitIcon
ImageLibrary
InfoPanel
InstantCraft
ItemSkinRandomizer
Kits
LoadingMessages
NoEscape
NoGiveNotices
NTeleportation
PlayerTracker
QuickSmelt
RandomSpawns
RemoverTool
RustRewards
ServerRewards
Skinbox
StackSizeController
StaffRoster
UCLANSUI
Vanish
Voter
Welcomer
WipeKits

When this happens, the data file is not in the correct json format. As in, you probably forgot a comma, or a quote at the end of the line while editing stack sizes manually. You can use https://jsonlint.com/ to check for any json errors in your data file.