Dell Force 10 and Cisco Nexus

Hi

I would like to request your assistance, I have connected a Dell Force 10 switch to a Cisco Nexus 5K, the Nexus has MSTP and the Dell has the default spanning tree, once I connect the Dell to Cisco the ports are blocked.

I checked this link

hasanmansur.com/.../

Please help me to resolve this problem. 

Thank you