From the Word vba help file:

This array is fixed or temporarily locked (Error 10)

You attempted to assign a value to a Variant variable containing an array, but the Variant is currently locked. For example, if your code uses a For Each...Next loop to iterate over a variant containing an array, the array is locked on entry into the loop, and then released at the termination of the loop
...
Use a For...Next rather than a For Each...Next loop to iterate. When an array is the object of a For Each...Next loop, you can read the array, but not write to it.

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Cheers,
Paul Edstein
[Fmr MS MVP - Word]