Project crashes @ Startup - VTStacks.Num

After sorting my “Tree” Folder with Mashes, Texures to a new place and restart my Engine i get this failure on startup:
“Assertion failed: VTStacks.Num() == MaterialCompilationOutput.UniformExpressionSet.VTStacks.Num”

Can´t Start my Engine and my Projekt anymore.

Ideas to Fix it?