GCD 5 is built on a combination of our own algorithms, ArcGIS functionality and ArcObjects. The advantages to providing this tool within ArcGIS are that it is a familiar analysis environment for many users, and users can then combine and leverage the many other capabilities of ArcGIS. The major disadvantage is that the GCD extension inherits a large number of unreliablities from ArcGIS (and some are our fault too). Before reporting a bug, we ask that you browse through this list to see if the problem you are experiencing is already logged.
To report a bug, visit our User Reported Bugs forum