SQL 2008 Express Auto Installation Failed - Process exited with code -2068052081

Hi
We've written a small ClickOnce project that "tries" to install SQL 2008 Express and it's prerequisites (.Net 3.5 sp1, Windows installer 4.5). In-house testing was great but in a live environment we find that the SQL install fails pretty much all the time.
Log below - "Process exited with code -2068052081" - are these codes documented anywhere / anyone have a clue what it means ?
Also seen this error code on other  PCs : "Process exited with code -2068578304"
Thanks, Grant
'.NET Framework 3.5 SP1' RunCheck result: No Install Needed Running checks for package 'SQL Server 2008 R2 Express', phase BuildList Running external check with command 'C:\Users\ic\AppData\Local\Temp\VSDE43A.tmp\SQLExpress2008R2\SqlExpressChk.exe' and parameters '10.50.1600 1033' Process exited with code 1 Setting value '1 {int}' for property 'SQLExpressChk' The following properties have been se ...