I open a case at PayPal support and i got this answer from them:
"I have checked our flow logs am I see that the issue with the language encryption is solved.
Also I see that for some transaction we receive a Validation_Result=Incorrect Signature;
which means that cryptographic hash we've stored for that IPN, doesn't mach one we receive back from your IPN listener.
You have to get in touch with your developer to check your IPN listener and see why it returns this Validation Result."
The problem I having is that some but not all PayPal Transaction stay at the pending state after successful payment and I get the error mail from the Virtuemart PayPal plugin.
Any help from the Developers will be highly appreciated.
Thank you.
I think we must first know the language you are using for your shop.