Nothing is perfect, and Behold may have some programming errors in it. If you encounter an internal error (which can be an out of range message or something like that), then an Internal Error window as shown here may pop up.
Internal Error Information
This shows what the error is, where in Behold it occured, and also has information about the Operating System and the version of Behold. This will help to track down and correct the error.
If you get one of these Windows, I'd very much appreciate it if you would take the time to send it to me so that I can try to fix the problem so that it won't occur for you or anyone else in the future.
Once this error window occurs, it is possible that some of Behold's memory space has been compromised. You can try to continue, but depending on the severity of the error, other problems may occur and some functions in Behold may cease to work. Your best bet is to exit Behold and restart. That will clean up the address space and everything should be fine again.
If the same error continues to occur, then it is definitely something that needs to be fixed in Behold. Please let me know about it.