Shibboleth SP "Metadata instance was invalid..."

[Bartlomiej Czesak]

Hello,

I'm having problem with connecting my IDP to SP. Both are Shibboleth 
instances. I have uploaded SP metadata to IDP and it seems to be working 
properly. I also have uploaded IDP metadata to SP, but my IDP doesn't 
show on the IDP list. I think important thing is that SP is 2.6.1 and 
IDP is 3.4.1. On the SP side, logs are telling me that metadata instance 
was invalid at the time of acquisition. Is there any way to use 2.x SP 
with 3.x IDP?

Best Regards

B.C.