When I hear people talk about a cake sliding or collapsing, it often involves strawberries. Whether it's strawberries that have been sliced or strawberry preserves, a strawberry is a slippery little devil.
First, never use that strawberry sleeved filling stuff. Or any sleeved filling for that matter, but that's another issue. The strawberry sleeved filling is seriously slimy and can let the layers shift.
Next, if you use preserves, do a THIN layer. Strawberry preserves is a lot of jelly and mashed fruit and too much will also be slippery.
When I do sliced strawberries inside a cake, I start with one layer of strawberry buttercream as a waterproofing method. The buttercream will prevent any juice in the berries from soaking into the cake.
After icing the layer, put a layer of sliced berries on the icing and press it into the surface to stick them in there. I use one of these slicers to get even thicknesses of berries: Strawberry slicer
Finally, take more buttercream and use it like grout in the cracks between the berries. You want the surface to be flat so that the berries are stuck in there and the top layer sticks to the icing, not the berries. That will help hold it in place and keep it from slithering away.
Once that's done you can put the top layer on and ice the cake. The berries won't shift around and it will be highly unlikely that your cake will do a slider.
Kara Buntin owns A Cake To Remember LLC, online cake supplies at www.acaketoremember.com and www.acaketoremember.etsy.com