Hi, I have the same problem. It occurs if more complex
dynamic expressions are used and the grid is being unloaded
e.g. the form is being closed.

It seems that from time to time the following happens due
to a VFP6 bug: some objects refered to in the dynamic
expression are already deleted from memory. If you use an
expression like DynamicForeColor=THISFORM.mycolor
OR DynamicForeColor=IIF(THISFORM..
you run into these errors.

I'm still looking for a solution. If you have already one please
let me know. One possibility is to reset all dynamic expressions
before a form is unloaded. The problem is that this could be a lot of work.
Creating an array of all objects through the complete
hierarchy (e.g. using the standard sample of MS or Autosize - you will have already one), look for grids and reset the expressions.
The problem is that it could not be tested before the work because it
is not possible to reproduce this error.

Andreas