Xcelsius 2008 applying service pack

We have excelcius 2008 (version 5.0.0.00 build 12,1,0,247 abd trying to apply lastest service pack (sp3). I sequence through the wizard until the window that that sates its is checking available disk space. It doesn't complete past this, stays at this screen for hours. Task manaer shows it is running and that it is not in the 'not responding state'. Have re-tried several times.

PC has huge amounts of free space.