In most cases, you might just need to download the Assets again - there is a very easy way to do this. Simply delete the folder %temp%\Enscape\Assets and restart Enscape. You can also find the folder via this path:
C:\Users\%username%\AppData\Local\Temp\Enscape\Assets\
If the issue persists, make sure you are not using our Offline Asset function. If you are, try turning the function off, as this will also trigger a re-download of all Assets.