Complex sentence: After an unsuccessful application to re-join Inverness, he was appointed manager of Livingston on 15 February 2006, after the resignation of Paul Lambert but was removed as Livingston manager on 15 April 2007 after a poor season in the First Division.
Split into simpler sentences: After an unsuccessful application to re-join Inverness, he was appointed manager of Livingston in February 2006, after the resignation of Paul Lambert. Robertson was sacked by Livingston in April 2007 after a poor season in the First Division.