HI
Can't say why what you are doing isn't working.
I find slideshows work as follows (for me at least)
Get (crop) your images into the same format as your VP frame 1:1.777 (1920 x 1080 or 1280 x 720 etc.) or you will have black bars either at the top/bottom or left/right of your film frame. Size in MP does not seem to matter, mine are 12 mp images in JPG format
Add them to the media list along with your mp3 file and then drag them onto the sequence line and the mp3 onto the Soundtrack 1. Add a title overlay etc to your first/last image
Check it plays as you want it to.
Click the "Save movie" toolbar tab.
Click "Computer/data"
Browse to your output folder and select it. Enter a name or accept the default.
I output as an avi file 1280 x 720 HD-720p and 25 fps. So select these values.
Click the "Encoder options" button
I use H246 (native) as the video compressor, so select this.
Set the "Video compression settings" slider to 23. Higher than this rendering is faster but the definition is worse, below this definition is better but rendering takes ages. 23 is a good average. Click OK
Set "Sound compressor" to MP3 (Native)
Sound format to 44100 Hz, 320 kbs
Click OK
Now click OK at the bottom to render your film into the selected folder.
Depending on its length it may take some time.
This avi should play OK.
Hope this helps
Nat