actually.... i'm in the first sketch when this error occurs. my cross-section is quite complicated. there are several hollows in the section. does that mean that it will not let me do a swept blend with a sketch that is not solid?
It is possible you have more than one of the same entity chosen. Example: Choose the same edge twice. In a complicated sketcher section this can cause problems because you must now diagnose each sketcher entity to see if one is on top of another. It also could be non-intersecting entities, in which case, trim corner might help. I agree for complicated sections use multiple datum curves to replace complicated sketcher sections and complete the feature using one or more curves you have sketched.