We have seen this before, where there is some junk left over from a VFP9 beta installation. Try this, it has worked in previous occurances of this error:

1. Uninstall VFP9.
2. Reinstall VFP9.
3. Reapply the SP.

>I'm trying to install the VFP 9 SP1 beta and it seems to refuse to install itself on my machine. It fails with,
>
>"The upgrade patch cannot be installed by the Windows Installer service because the program to be upgraded may be missing, or the upgrade patch may update a different version of the program. Verify that the program to be upgraded exists on your computer an
>d that you have the correct upgrade patch."
>
>VFP 9 is definitely installed. I looked in the event log and it references an MSI log file (I hate MSI when things don't work...). Here's part of it,
>
>MSI (c) (48:98) [10:20:58:515]: Note: 1: 2205 2: 3: MsiPatchSequence
>MSI (c) (48:98) [10:20:58:515]: SequencePatches starts. Product code: {9BAAE963-E16D-4E17-AFE6-1965F5AA0292}, Product version: 9.00.1720, Upgrade code: {B2BD6124-22F7-45D1-AFA6-65F8500EB19D}, Product language 1033
>MSI (c) (48:98) [10:20:58:515]: Note: 1: 2262 2: _Columns 3: -2147287038
>MSI (c) (48:98) [10:20:58:515]: Note: 1: 2205 2: 3: MsiPatchSequence
>MSI (c) (48:98) [10:20:58:515]: Note: 1: 2205 2: 3: MsiPatchMetadata
>MSI (c) (48:98) [10:20:58:515]: Note: 1: 2262 2: _Columns 3: -2147287038
>MSI (c) (48:98) [10:20:58:515]: Note: 1: 2205 2: 3: MsiPatchSequence
>MSI (c) (48:98) [10:20:58:515]: Note: 1: 2205 2: 3: MsiPatchMetadata
>MSI (c) (48:98) [10:20:58:515]: 2.0 patch C:\DOCUME~1\PMROZO~1\LOCALS~1\Temp\IXP000.TMP\VFP9.0sp1-KB906478-X86-Beta-Enu.msp of type minor upgrade takes product {9BAAE963-E16D-4E17-AFE6-1965F5AA0292} to version 9.00.3307
>MSI (c) (48:98) [10:20:58:515]: PATCH SEQUENCER: verifying the applicability of 2.0 minor upgrade patch C:\DOCUME~1\PMROZO~1\LOCALS~1\Temp\IXP000.TMP\VFP9.0sp1-KB906478-X86-Beta-Enu.msp against product code: {9BAAE963-E16D-4E17-AFE6-1965F5AA0292}, product version: 9.00.1720, product language 1033 and upgrade code: {B2BD6124-22F7-45D1-AFA6-65F8500EB19D}
>MSI (c) (48:98) [10:20:58:515]: Validating transform 'T1350_1ToU1' with validation bits 0x923
>MSI (c) (48:98) [10:20:58:515]: Note: 1: 2749 2: T1350_1ToU1 3: C:\DOCUME~1\PMROZO~1\LOCALS~1\Temp\42edfdd.msp 4: 9.00.2412 5: 9.00.1720
>MSI (c) (48:98) [10:20:58:515]: 1: 2749 2: T1350_1ToU1 3: C:\DOCUME~1\PMROZO~1\LOCALS~1\Temp\42edfdd.msp 4: 9.00.2412 5: 9.00.1720
>MSI (c) (48:98) [10:20:58:515]: PATCH SEQUENCER: 2.0 minor upgrade patch C:\DOCUME~1\PMROZO~1\LOCALS~1\Temp\IXP000.TMP\VFP9.0sp1-KB906478-X86-Beta-Enu.msp is not applicable.
>MSI (c) (48:98) [10:20:58:515]: SequencePatches returns success.
>MSI (c) (48:98) [10:20:58:515]: Final Patch Application Order:
>MSI (c) (48:98) [10:20:58:515]: Other Patches:
>MSI (c) (48:98) [10:20:58:515]: Unknown\Absent: {A084F879-D79E-4D0C-84B8-D697A0C8D92D} - C:\DOCUME~1\PMROZO~1\LOCALS~1\Temp\IXP000.TMP\VFP9.0sp1-KB906478-X86-Beta-Enu.msp
>The upgrade patch cannot be installed by the Windows Installer service because the program to be upgraded may be missing, or the upgrade patch may update a different version of the program. Verify that the program to be upgraded exists on your computer an
>d that you have the correct upgrade patch.
>c:\windows\Installer\5296d58.msi
>MSI (c) (48:98) [10:20:58:546]: Product: Visual FoxPro 9.0 Professional - English - Update '{A084F879-D79E-4D0C-84B8-D697A0C8D92D}' could not be installed. Error code 1642. Additional information is available in the log file C:\DOCUME~1\PMROZO~1\LOCALS~1\Temp\MSIedfdc.LOG.