Just to be clear, it's not 12megapixels that's the issue (we allow up to 48 megapixels) ... it's that his files are over 12 megabytes each - and for standard and power accounts we allow up to 12 Mb, Pro accounts up to 24 megabytes.
What JPEG compression level are you selecting for the export/upload? With a proper compression level (~85% on the 1-100% scale or level 10 on the 1-12 scale), you should have no problem uploading 12 megapixel images.