You mention the most common reason for a shape failing to solidy/thicken.
Look out for very tight curves and also the control frame overlapping. If solidify wont work try thicken with a very thin section. Creo should thicken most of the model (grey) but not the problem areas (blue) which help focus in on the surfaces that need tweaking..
I tried downloaded the zip file to take a look but the part had the wrong extension.
Try uploading the native Creo part file and I will have a look.