There are never any absolute negatives in investing. It's a warning flag is all. Sometimes management changes completely and it really is a new company, and sometimes the name change is justified by a change in focus.
For example, Trillium legitimately changed its name from Stem Cell Therapeutics.
And sometimes companies can simply change dramatically. There is no better example than Pharmacyclics - they in fact never changed their name, but I wouldn't have blamed them if they had!