[hbear]

I have a sizeable list of citations at the end of a paper I'm working on.
References within the text are cross-referenced to this numbered list. My
problem is that the list has to be updated fairly frequently, with additions,
deletions, and cut and paste reordering. Sometimes these changes are dealt
with appropriately during field updates, but at other times, apparently at
random, I receive the error message "Error! Reference source not found."
Could someone explain what generates that error and how I can ensure that
the cross-references will work while still allowing me to organize and update
my list as needed.