If I enable ground shadows I get these strange squares on the runway grass or ground areas, anyone know why, or what they are supposed to be a shadow of?

Looks like an issue with cloud textures and/or shaders corruption. 

If you are using a 3rd party cloud texture, re-install or re-apply the textures. Also, clear the shaders folder. It's been a while since I've done this in FSX but it will easily google.

Good luck. 

Edited July 17, 20223 yr by hs118

Shadows are nice, but I never found them to be 100% reliable in FSX.  Oddities can occur with shadows, they are a drag on system performance and not all objects cast a shadow.  I don't use the DX10 Preview mode, but if FSX is in DX10 Preview mode, you can have all sorts of issues unless you also run Steve's DX10 Fixer software.

Edited July 17, 20223 yr by stans

Unless you use Steve's Direct X 10 Fixer and his Cloud Shadows addon, there are no cloud shadows in FSX.
Most likely, the random squares are just a symptom of the FSX ground shadows that were and still are broken.
The best solution is to switch them off.

If you feel the need to delete the shaders, they are to be found at C:\Users\User name\AppData\Local\Microsoft\FSX and 
the Shaders folder(s) can be deleted. FSX will rebuild them when it is next run.

This is in DX9 btw, so yeah, guess its just a typical FSX glitch thing or aliens.

Interesting I didn't know DX10 FSX could have cloud shadows now with Steve's fix.

 

 

Aliens?