Selecting columns in table gives 5992 error

I have used the VB editor in Word 2000 to create a class that adds columns to
existing tables and sets text in the new column cells based on the contents
of the existing cells in the neighbouring column.

To Insert Column:

Create column object
Select it
Insert new column

Set oColX = TableX.Columns(lngCol)
oColX.Select
Selection.InsertColumnsRight

All went well till the program encountered a table split over multiple pages.

I then got run time error 5992 ..... cannot select.... column has mixed cell
widths!

So

a) how do I con Word into letting me select a column to insert a column
after it

or

b) how do I insert a column where the table is split over a page split?

Anybody solved this problem before.

Thanks