Installation of SP1 for SharePoint Foundation failed

I installed SP1 for SharePoint Foundation yesterday on a brand new insatllation and encountered no problems at all. Today I’ve attempted to install it on another SharePoint Foundation enviornment but this one has a handful of custom Features installed but basically no content loaded. The installation ran fine but I hit a problem when running the config wizard at step 10 (the final step). The progress dialog displayed progress until it reached around 91 percent complete i.e.

The farm is being upgraded in the timer service process. The task is 91.28% completed.

before it failed with the ambiguous error message:

An exception of type Microsoft.SharePoint.PostSetupConfiguration.PostSetupConfigurationTaskException was thrown.  Additional exception information: Failed to upgrade SharePoint Products.
One or more configuration settings failed.  Completed configuration settings will not be rolled back.  Resolve the problem and run this configuration wizard again. 
The following contains detailed information about the failure: <log file detail>

I examined the upgrade log file to try and determine what had caused the failure and found the following error:

SyncUpgradeTimerJob: Upgrade timer job failed. Return -1.
07/06/2011 11:25:33  12  ERR                  The exclusive inplace upgrader timer job failed.

There was nothing further to indicate in this log file what caused the problem. At this stage, as far as I can tell everything is working ok, I can still access the site collection and Central Admin running on the server. Given the problem seemed to be a failure of a timer job I reviewed the status of the Upgrade Time job and found that it has its own log file. Upon reviewing this timer job’s log file I found the cause of the failure of the Upgrade timer job:

[OWSTIMER] [SPContentDatabaseSequence] [ERROR] [7/6/2011 11:23:07 AM]: Found a missing feature Id = [e2bd7171-e179-451d-b6b1-6d15a0297e41], Name = [Custom Feature 1], Description = [This feature requires that the Custom Feature 1 feature is enabeld to ensure that all sub sites inherit the required master page.], Install Location = [My.SharePoint.Feature]
[OWSTIMER] [SPContentDatabaseSequence] [ERROR] [7/6/2011 11:23:07 AM]: The feature with Id e2bd7171-e179-451d-b6b1-6d15a0297e41 is referenced in the database [WSS_Content_DB], but is not installed on the current farm. The missing feature may cause upgrade to fail. Please install any solution which contains the feature and restart upgrade if necessary.

So it appeared that it was apparently related to a missing custom feature. After a few checks I ran the config wizard again and it completed successfully and when I checked the upgrade status in Central Admin it shows that the upgrade to SP1 has completed successfully.