error: MLAB cell is driven by combinational sources on Port A

I compile an IP using synplify, and get a .vqm file.

Then put the .vqm file into a quartus ii project to synthesize and fit.

When the version of quartus ii is v14.0, it works well.

When the version of quartus ii is v11.0, it reports one error at fitting phase.

The error is:

mlab cell ...... is driven by combinational sources on port a

What is the reason? Can anyone help me?

:(:(