Transferring Power BI dataset to dataflow, getting Token Eof expected error on custom column

Hi All

I am transfering a large dataset that takes ages to refresh in PowerBi desktop to a Dataflow on the PowerBi online service. I have the follwing Custom Column in my current desktop quiery.

This works fine in the desktop but when I add the same column in the Dataflow UI I get the a warning of 'Token Eof expected'.

(Please note, some of the column names are different below but are correct to the columns in the Dataflow table).

The error seems to be with the var '_newavg'. I've tried chaging the var name but get the same error. 

Any ideas what's causing this?

Thanks

Thom