Exporting images from Ps back into Lr

Hi, just sent a panorama image of 314,415,236 pixels (15 shots) to Ps for editing. Lr sent the large file to Ps no problem.

I'm finished editing in Ps and want to return the file back to Lr. I get a warning that Ps cannot export the file because it's too big. (Bottom left of the image says the file is "Doc: 1.61G/3.124G".)

My question is : how can Lr export the file but Ps cannot send the same back? If there's a fix maybe someone could share.

Thanks 

Allan Wiggins