Performance of 1394 devices may decrease after installing Windows XP SP2, XP SP3 or Vista.
The problem occurs if you connect a 1394a or 1394b FireWire device to a 1394b bus, or a 1394b device to a 1394a bus. Specifically, Windows XP Service Pack 2 and Service Pack 3 incorrectly force S800 (1394b) and S400 (1394a) nodes to S100 speeds while Windows Vista forces S800 (1394b) nodes to S400 speeds. The following Microsoft knowledge base article explains the problem for Windows XP Service Pack 2 users, and provides a Hotfix designed to enable devices that run at S400 speeds to operate correctly:
It is important to note that initial test results show that devices running at S400 speeds (400Mbps) operate correctly using the Hotfix. However, devices running at S800 speeds do not operate correctly using this Hotfix.
Workaround #1 - Downgrade the Windows 1394 Drivers
As an alternative workaround to this issue, users can downgrade to the 1394 drivers that come with Service Pack 1. It can be run against Windows XP SP2 or SP3.
Note: If the Automatic Updates feature of Windows Update is enabled, your drivers downgrade may be reversed without any notice. To turn off Automatic Updates, log in to your machine as an administrator, open the System tool from the Control Panel, and click the Automatic Updates tab.
This can be done manually using Windows Safe Mode. Please note, if the Windows File Protection service is enabled, it will not allow the 1394 drivers to be replaced.