What version of Premiere Elements? What computer operating system?
From your specific issue I am almost certain that you are using Premiere Elements as a 32 bit application and probably running Premiere Elements 9.0/9.0.1 or earlier.
If this is the case, there is nothing you can do but to reduce the total pixel count for the jpeg. I have written about this before when it was involved in a Premiere Elements 8.0/8.0.1 issue.
Please see the full story in post 6 of the following
Please consider, give more details, and I will go into this matter specific to your situation.
In my books, I recommend that any photo you load into Premiere Elements be sized to no larger than 2000x1500 pixels (72 ppi).
Using a larger or higher resolution photo will not give you more detailed or higher quality slideshow. Video resolution is video resolution, and the closer your photo is to video resolution, the better it will look.
Detailed information when you are going through the "do not exceed" choices for pixel dimensions.
Remember, the key factor is not pixel dimensions but rather total pixel count as detailed in the link that I have already provided.