Cant load level from 4.8 preview 3 into preview4

Hi,
I am working on a project and have saved my levels in 20 different progress stati in version 4.8 preview 3.
now i updated to the latest 4.8 preview 4 (31.May 2015) and cant load the levels from save 5 on upwards.
The Editor crashes during loading and gives me just the options to
-search online for a solution (yields nothing)
-end
-end and debug, which starts vidual studio but my 30 day trial has expired.

what can i do to safe my work, as i cant even load a converted copy in 4.7.6.
is there a way to focus that error, or fix it? i assume i brought some textures in at that stage of the level, but i changed a lot, so i can not tell what differences are there between level safe 4 and 5

greetings!