Paypal Error - Invalid Token

I am experiencing the error below on a live site when customers choose paypal as form of payment.
I am using Nop 1.6
It was working fine for the last year the error just happened.
All settings  (API etc) were working fine and no changes have been made to NOP cart.
Can anyone help me with figuring out what the problem is and how to fix it?


NopSolutions.NopCommerce.Common.NopException: LongMessage: Invalid token. ShortMessage: Invalid token ErrorCode: 10410 at NopSolutions.NopCommerce.Payment.Methods.PayPal.PayPalExpressPaymentProcessor.GetExpressCheckout(String token) in F:\Temp\Test\nopCommerce 1.60\Payment\Nop.Payment.PayPal\PayPalExpressPaymentProcessor.cs:line 239 at NopSolutions.NopCommerce.Web.PaypalExpressReturnPage.btnNextStep_Click(Object sender, EventArgs e) in F:\Temp\Test\nopCommerce 1.60\NopCommerceStore\PaypalExpressReturn.aspx.cs:line 50

Just an update what Paypal has seen as the cause of this:
"As you can see there, your shop is submitting the token "ec-3cu0000wt...." all in lowercase. Our TOKEN is case sensitive and it must be submitted in the way you received it from us, so all in Upper Case characters.

I would suggest here to contact NOPcommerce directly. My colleagues there should be able to help you fixing this issue in their Software. Once your shop is submitting it all in upppercase, you won't receive that error-"


Could anyone please tell me where n how i could  fix this error?
Thanks in advance.

Anyone?

It seems to me that i have to change the Token to TOKEN but so far i had no luck
Which file/s do i have to change the Token into caps?