Windows 7: Event viewer error & warning during SP1 install

Earlier today I used Windows Update to install SP1 on two more or less identical computers with Windows 7 Home Premium 64-bit. Before I did it I checked everything that MS advise, and all was OK. Both computers show that the installation was successful, and the system information confirms that they have SP1.

However, on one of the computers only the following error and warning are showing in the event viewer, from around the time the actual installation started (ie immediately after the download completed):

Error - Source VSS, Event ID 12305 Task Category None:

Volume Shadow Copy Service error: Volume/disk not connected or not found. Error context: DeviceIoControl(\\?\GLOBALROOT\Device\HarddiskVolumeShadowCopy18 - 000000000000012C,0x00560034,00000000002F0FE0,0,00000000002EFFD0,4096,[0]).

Operation:
Processing PostFinalCommitSnapshots

Context:
Execution Context: System Provider

______________________________

Warning - Source Ntfs Event ID 57 Task Category (2)

The system failed to flush data to the transaction log. Corruption may occur.

(end of messages)

Both messages showed exactly the same time. System restore shows that a restore point was created at the same time, which suggests that it did manage to create a restore point despite the error.



I tried restarting the computer, and it didn't try to run chkdsk (which I would expect it to do if there were any disk errors, and which has been mentioned elsewhere). Disk management shows all disks and partitions to be healthy (before and after the restart).

Please can anyone tell me what's going on and if I need to worry about it? Many thanks.