Windows does not recognise LPC-Link
There is a bug in Windows that may occasionally cause it to not recognise the LPC-Link (LPCXpresso board) when starting a debug session.
See the following Microsoft Knowledgebase for a description of the problem and workarounds: http://support.microsoft.com/kb/817900
Additional notes: The Microsoft article states: "If you quickly and repeatedly insert and remove a USB device, the USB port may stop responding. When the port is in this state, it no longer recognizes any USB device, and the USB device will not work."
After initialising (booting) the LPCXpresso board with the debug firmware, it disconnects from USB and then reconnects very quickly, and thus can provoke this issue.