What mission is it? ive looked through list and don't have any with power struggle
The mission 'Power Struggle' is one of the Calypso Gateway ones.
I seem to recall some of the Gateway missions were changed, sometime after the ones on Entropedia were added.
Check the list of missions in that series (http://www.entropiawiki.com/Info.aspx?chart=Mission&name=Power_Struggle) - perhaps it's previous (or next) one that you need to abandon?
Another thought is that the 'Power Struggle' mission has been renamed - so perhaps check for one with similar objectives.
Are you able to see Gateway missions while on Calypso?