The following images will be rendered at less than 300 dpi at the requested print size.

Bearing in mind this is now an old post. For anyone that comes across this problem in the future, and if its any help. I regularly print large panoramics using an Epson P800 and almost always comes across this message. If just go ahead and send your photo to print and then after it has printed, when you go to close the image rather than press "dont save" press 'save this image" when you reopen the image you should notice if open the resize dialogue box that the ppi resolution remains the same. 

I hope this reassures some of you. For sizing images you should go on the Marrutt website where there is a tonne of info on these matters

Regards Mirek

"The following images will be rendered at less than 300 dpi at the requested print size.' I don't know where to go to correct this or stop this warning message. Please help! Jo-Anne

You can ignore this pop-up. Your prints will come out ok.

See this discussion:

the following images will be rendered less than 300dpi | Photoshop Elements & More