Data Grids Stop Working

[Paul Looney]

Many times, on many stacks, data grids have simply stopped working -  
without any warning or error.
The line of code they fail to execute is this, or similar:

    set the dgText of grp "Data Grid" to vTheList

The code may have worked for months before is fails.
The only solution I've found is to delete the existing grids and  
replace them with new ones. Doing so, without any code changes, fixes  
the problem.
I don't have a recipe. But, so far, the problem has only come up  
while working in the IDE.
It has appeared on different computers (all Mac), with different OSes  
(OS X 10.4.11 through OS X 10.6.4) and assorted versions of Rev/ 
Livecode (4.0 through 4.5.1).
Advice/suggestions appreciated.
Paul Looney