Spreadsheet Question - how to total a Time column

I've got a column of hours and minutes (00:00) I'm trying to total. Each cell is the result of a start and end time that works fine.

What I can't get is a result once the total exceeds 24 hrs. I've tried -
<ul type="square"> =SUM(C.1:C50)[/list]and get "#####" as a result.

I checked the first few cells (less than 24 hrs total) and it works.

Any suggestions? Thanks.

[img]/images/graemlins/confused.gif[/img]