Marketpress currency issue with Paypal

My store has been working perfectly but id noticed a few store owners had used a different currency which didn't convert properly when the sale was made. So, I removed all of the currency options apart from GBP which is the only currency I want to accept but now I'm getting this error at checkout:

There was a problem connecting to PayPal to setup your purchase. Please try again.

559044 - The receiver does not accept payments in this Currency

Not sure what the problem is. Is it an issue with my API, Database or Marketpress?