Creating a print file in A0 not working

[Adam5E12]

Hi there let me just cut to the chase. 

Im a learning photographer and i use photoshop for editing and handling my images. I have just got an order for one of my images in the size of A0. I looked up the size of the image online dimesnsions for A0 being 14043x9933px and i put that in manually. The file is made up of the image with a 10px stroke on it and the base layer. 

When i go to export my image photoshop scales it down from 100% to 84% saying ive exceeded the maximum limit of pixels (Which i thought to be 300'000x300'000px). The image is 300ppi. 

The exact message it gives me if i try to scale up is "The image dimensions cannot scale exactly as entered and have been rounded. For an exact size, please use Canvas Size or scale the layer and layer effects in the document."

I have tried altering the canvas size and i have messed around with lower ppi settings (100, 200, 250) and nothing has worked so far. I have taken off the stroke from the image and that didnt work either.
Any and all help is appriciated.

[JJMack]

A0 paper size 841 x 1189 mm you image needs to have an aspect ratio like that paper's 841:1189 aspect ratio.    Crop your image (any image size) so its aspect ratio is correct for that paper then set its print resolution to print on that size paper.

[Adam5E12]

Thank you for your very fast and detailed response!
I have attempted what you have suggested and this still hasn't resolved my issue.

I dont know if this effects anything but the scale simply won't go to 100%.

[JJMack · Accepted solution]

Do not use export use save as.  Export is for the web and has some preconceived notions about what it should do to your images.

[Adam5E12]

Fantastic! Thank you very much for your help! 

[davescm]

As JJMack says, the export functions are for Web use and limit the pixel size. Use Save As.

Dave