Any One Now How To Fix this prb?

first : Happy New Year for every one ;)

I made a War system but there is a problem when

i open the game and open the NPC and click on the "register in the war" bottome
these message came :
Attempt to perform arithmetic on a string value

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This is secret project, if one knows the solution add me on Skype to tell him all the details
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my skype : mohamad512-aboatallah


thanks

try tonumber() function for your values.
if dont help, make sure there are no nil values or there is no character except numbers