Infill not Slicing/printing

[will4836]

Hi all,

I have just begun using S3D and am having an issue with my print. I am trying to print a part for a model airplane which has thin 0.4mm walls. However, there are some areas that are solid which I would like to have infilled. For some reason these areas will not slice with any infill though - they are just hollow.

Any suggestions? I have attached the STL file below (for some reason I can't attach the IPT file - any thoughts?)

Any help is very appreciated! Thanks - Jim