Problems with FT245BL

Hello!

I've developed a board with an USB-Interface (USB-To-Parallel) using the 
FT245BL from FTDI.
But my Windows-7-PC claims after connecting the board (for testing 
without the main-µC), that the hardware isn't properly working and it's 
listed as unkown device.

I've attached the accordant circuit diagram.
C4 and C5 are both 27p ceramic-capacitors.
The power is taken by an external power-supply (USB Self-Powered 
Configuration).

At my first attempt I used by mistake a 16 Mhz quartz anstead of 6 Mhz.
Between AVCC and +5V I've later added a 500 Ohm-resistor.

However, it isn't working - could have the missing resistor or the wrong 
quartz destroyed the FT245BL?

My power-supply displays, that the FT245BL draws 20mA when it isn't 
connected to the pc and 0mA (yes, really zero) when it is (at the moment 
of connecting it increases for a very short time to about 60mA).

I've no idea how to locate or to fix the problem, general how to 
approach.

Thank you for help,
Henning