UDF Causes #value Error Whenever Copying Cells

1) The following code works well except for 1 wierd circumstance. This UDF code resides in a Cell in workbook 'A'. If I have another workbook open (call it workbook 'B'), and I do ANYTHING in workbook 'B' (like copy a cell to another cell within workbook 'B', or perform a calculation within workbook 'B', or even copy a cell from 'A' to 'B'), then the cell that this UDF resides in (workboook 'A') will change from a good number to a #VALUE error. If I work ONLY within 'A', then this UDF functions properly (giving a good result).

2) If I hit the F9 button (i.e. re-calc), with workbook 'A' active, then the #VALUE goes away, and the good number comes back. To clarify, all workbooks have AUTO CALC enabled. I guess the 'Application.Volatile' line causes this code to run when I hit the F9 button (thereby clearing the #VALUE error). If I hit F9 with 'B' active, then the #VALUE error (back in 'A') goes NOT clear.

3) NOTE #1: If I put a BREAKPOINT inside this code, and then repeat a "copy from cell to cell" within workbook 'B', I find that the following code DOES NOT execute, as it does NOT "stop" the code at the BREAKPOINT line. But, when I hit F9, then it DOES stop at the BREAKPOINT.

4) NOTE #2: If I "comment out" the Application.Volatile line, it still does the SAME thing. Except worse, then when I hit F9, it doesn't correct the #VALUE error. I really need the Application.Volatile step with this code, as these functions will not automatically update if their referenced cells are changed.

5) NOTE #3: The variables Row_Num & Column_Num are declared at the Module Level. If I use unique variables and declare these at the Procedure Level, it makes NO difference. I also tried putting a "DoEvents" line after Application.Volatile, but NO difference.

6) It seems I need this code to execute whenever there is a "change" on ANY workbook. Or else, do something to keep these cell values from changing anytime there is "action" on another workbook. Or, is there better code to do the samething? ... Do you have any CLUE how to fix this SNAG?