wdLineWidth050pt has a value of 4
wdLineWidth150pt has a value of 12

So it appears you can't type in a value in points and expect Word to be able to assign that correctly to the LineWidth property. The only acceptable choices in that series of constants are:
2, 4, 6, 8, 12, 18, 24, 36, 48

You can review these constant values by using the VBA editor and going to View>Object Browser and searching for wdLineWidth which is the common prefix for all the possible relevant constants.

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Andrew Lockton
Chrysalis Design, Melbourne Australia