Dell Force 10 and Cisco Nexus

Hi

Please assist me to find the problem, I have connected a Dell Force 10 switch to a Cisco Nexus 5000, the Nexus is running MSTP and the Dell switch is running basic spanning tree, the problem is when they are interconnected, the ports are blocked, not sure if it is a problem of Spanning tree.

I was reading this article 

Between the devices we have a port channel.

Thank you so much