but get the error message "Unable to set the number format property of the range class".

Can you help?

A little - I spent about 20 minutes playing around with this and I hope that what I found out can point you in the right direction.

First of all, you need to reference a specific column in the columns collection like so:

loColumn = o.Application.DataSheet.columns( 'B' )

Second of all, "Accounting" is a custom format, so what MsGraph wants is a format string. When I recorded a Macro in Excel, and set the NumberFormat of a column to Accounting, this is what Excel generated:

Selection.NumberFormat = "_($* #,##0.00_);_($* (#,##0.00);_($* ""-""??_);_(@_)"

However, MsGraph did not like this format string. What you need to do is find the format string that MsGraph likes.