the Dreamweaver cache file is susceptible to becoming corrupted, any time a behavior is run in Dreamweaver, the behaviors code is compiled and stored in he dat file, this is an attempt by Dreamweaver to speed things up the next time that the behavior is run. That compiled behaviors can become unstable though quite easily and cause random errors to start occurring.
Deleting that file is always the first step in troubleshooting error messages in Dreamweaver.
Adobe has it listed at number 4 in their troubleshooting guide:
but it is one of the simpler things to try, so I always try it first.