What is the issue that you are facing when using full speed?
is it not enumerating? or data trasnser is not happening?
Please provide more details.
Can you provide the Isolator details?
Are you connecting FX2LP based device on the other side of isolator?
Please share your FX2LP project.
From the link http://www.saelig.com/MFR00151/UBUSB1001.htm it seems that it supports only Full speed.
I am not sure how it is working as High speed for you.
Are you connecting to full speed host?Which device you are connecting on the other side?
Your previous response doesn't give much information.