Error 10002 - paypal pro

I am testing my Paypal pro and i got the API signature and all from Paypal. I have the plugin on sandbox environment. when i try to process it says "Error 10002: Security header is not valid"

I changed the settings to production and tried a real transaction, so this time it worked!

Yes, here is more information for interested users:
www.hikashop.com/en/forum/4-how-to/31001...0is20not20valid.html