HP will scan wired to PC but not through router

[phkhgh]

Home network setup w/ Linksys WRT110. Can print to HP C5100 from wired desktop or wireless laptop.

If printer is hooked to router, HP scanning software says "Error communicating w/ scanning device."
Shut my FW/AV down & had no effect.

If connect printer to PC w/ USB, scanning software works fine. There's no problem printing over the network, so the printer has an IP address from the router (verified from printer).

Any suggestions? Thanks.

[PrntRhd]

From their site:
http://h20000.www2.hp.com/bizsupport/TechSupport/Document.jsp?lang=en&cc=us&taskId=110&prodSeriesId=1153538&prodTypeId=18972&prodSeriesId=1153538&objectID=c00897542
and
http://h20000.www2.hp.com/bizsupport/TechSupport/Document.jsp?lang=en&cc=us&taskId=110&prodSeriesId=1153538&prodTypeId=18972&prodSeriesId=1153538&objectID=c00654095