attempt to compare number with nil.

[Aristates]

Where The Problems ? debug say's ; :6 attempt to compare number with nil.

addEvent("AristatesOnServer", true) 
        addEventHandler("AristatesOnServer", getRootElement(), 
        function() 
                local Aristates = getPlayerAccount(source) 
                if Aristates then 
                    if tonumber(getAccountData(Aristates,"cash")) >= 50000 then 
                        setAccountData(Aristates,"cash",(tonumber(getAccountData(Aristates,"cash")) or 0)-50000) 
                    else 
                        outputChatBox ( "Yetersiz Para", source, 255, 255, 255, true ) 
                    end 
                end 
            end 
        ) 

[Fist]

if it is nil then player account data "cash" is nil.

if you want to dont give error until he gets actual money and saves it then use this code

  
addEvent("AristatesOnServer", true) 
        addEventHandler("AristatesOnServer", getRootElement(), 
        function() 
                local Aristates = getPlayerAccount(source) 
                if Aristates then 
if tonumber(getAccountData(Aristates,"cash")) == nil then return end 
                    if tonumber(getAccountData(Aristates,"cash")) >= 50000 then 
                        setAccountData(Aristates,"cash",(tonumber(getAccountData(Aristates,"cash")) or 0)-50000) 
                    else 
                        outputChatBox ( "Yetersiz Para", source, 255, 255, 255, true ) 
                    end 
                end 
            end 
        ) 

[Al3grab]

just add the 'or 0' next to the account data check

[jingzhi]

Where The Problems ? debug say's ; :6 attempt to compare number with nil.

addEvent("AristatesOnServer", true) 
        addEventHandler("AristatesOnServer", getRootElement(), 
        function() 
                local Aristates = getPlayerAccount(source) 
                if Aristates then 
                    if tonumber(getAccountData(Aristates,"cash")) >= 50000 then 
                        setAccountData(Aristates,"cash",(tonumber(getAccountData(Aristates,"cash")) or 0)-50000) 
                    else 
                        outputChatBox ( "Yetersiz Para", source, 255, 255, 255, true ) 
                    end 
                end 
            end 
        ) 

AccountData of "cash" is nil, maybe you didnt set it correctly