SOPC Warning

..... what the message really means is that you have a master that lacks the waitrequest signal. Waitrequest is used to tell the master that the fabric is not ready to accept a read or write request. Reasons for this blocking could be that some other master is accessing the slave or the slave can't accept any more transfers.

The Avalon spec states that waitrequest is a mandatory signal for any master in your system: http://www.altera.com/literature/manual/mnl_avalon_spec.pdf

So if you hooked up this problematic master to a slave that already has another master connected to it then the fabric would have no way to tell the master lacking the waitrequest signal to hold off. If you are familiar with shared bus interconnects waitrequest is very similar to ~master_grant.