Many times when trying to dig holes i get the error message "not hollowed out or to deep to dig". 

What is casuing this, I have tried this both by hollowingout the model in Chitubox or in other 3rd party programs. I can understand it when trying to dig a hole though a complex part of a model, but in some cases i can dig a hole though one side of the model but not the other even though they seem the same? 

This is really frustrating and prevents me printing some models.