Im trying to use the bevel option with the text tool (in the spline modeler) The model I get from this is giving me some problems becouse: 1-if I import the text from illustrator, some letters get a weird form. 2-if I write the text in carrara some letters get filled wrong, like the A in the inside. Why do I have this problem?

Especially for text, the bevel tool in the spline room should use small values like: .02 Otherwise, Carrara goes nuts because the bevels start overlapping and intersecting.

But it looks too small, I dont see the bevel with values like 0.02

It may be too small. Since I don't know the scale of your objects I can't provide you with an accurate number to bevel with. However, the problems shown in your images is a result of too large a bevel. Just incrementally reduce the size until it works.