SQL Express SP2 Upgrade Fails.

So I've tried today to upgrade a SQL Express instance on a machine where "proper" SQL has already been upgraded.

It fails.

The error code is 2259. Database: Table(s) Update failed

So I thought I'd uninstall SQL Express altogether and just do a full install. But it cannot find the MSI files to uninstall itself.

The part of the log file referring to it appears to be

<Func Name='ProcessHeaderTable'>
<Func Name='ProcessScriptTable'>
<Func Name='GetFileTargetPath'>
<Func Name='GetFileTargetPath'>
<Func Name='GetFileTargetPath'>
<Func Name='GetFileTargetPath'>
<Func Name='GetFileTargetPath'>
<Func Name='GetFileTargetPath'>
<Func Name='GetFileTargetPath'>
<Func Name='ProcessScriptTable'>
<Func Name='GetFileTargetPath'>
MSI (s) (B4!EC) [18:23:49:453]: Note: 1: 2259 2: 3: 4:
<Func Name='GetFileTargetPath'>
Error Code: 0x8007065b (1627)
Windows Error Text: Function failed during execution.
Source File Name: darlibviewinstaller.cpp
Compiler Timestamp: Wed Jun 14 16:19:22 2006
Function Name: sqls::ViewInstaller::modify
Source Line Number: 137



---- Context -----------------------------------------------


Setting status of unmanaged components and removing unmanaged resources
Failed to modify installer view
1: 2259 2: 3: 4:



Error Code: 1627
MSI (s) (B4!EC) [18:23:54:890]: Product: Microsoft SQL Server 2005 -- Error 2259. The installer has encountered an unexpected error. The error code is 2259. Database: Table(s) Update failed

Error 2259. The installer has encountered an unexpected error. The error code is 2259. Database: Table(s) Update failed
<Failure Type='Fatal' Error='1627'>
<EndFunc Name='LaunchFunction' Return='1627' GetLastError='203'>
Action ended 18:23:54: ValidateUpgrade.D20239D7_E87C_40C9_9837_E70B8D4882C2. Return value 3.

Anyone got any ideas?