HDL error at <location>: can't infer register for "<string>" because its behavior does not match any supported register model

(ID: 10821)

CAUSE: Quartus II Integrated Synthesis attempted to infer a register for the specified object in a design file. However, the behavior of the object is not compatible with any register model recognized by Integrated Synthesis. You might be attempting to infer a register using a coding style that Integrated Synthesis does not support, or you might be describing an object with functionality that cannot be represented by a hardware register.
ACTION: Consult the Recommended HDL Coding Styles chapter of the Quartus II II Handbook for more information on inferring registers, or use an existing template from the Insert Template dialog (Edit Menu) in the Quartus II GUI.

See also:

Design Guidelines for Using Quartus II Integrated Synthesis