Voltage level problem on a pin which is a clock

Hi all

The problem still occurs on my prototype

Here is today's diagnosis :

- The track has a length of 2cm. And in comparision whit datasheet, it doesn't seem to be an impedance adaptation problem

- I try on another prototype card, still unsuccesfull

- I cut the track just in front of the concerned pin, the clock stay between 0.7V and 1.8V

- The board is correctly routed, no false contact and all power (VccIO, VccInt, GND) have the good voltage

- Someone suggest me that the concerned pin has an special function "VREFB3N0", but i don't think that's a problem

- another tell me that another clock, which stay inside the FPGA, is a virtual clock, but on the dev board with the same programm it wasn't a problem

finally my prototype still not working but why ?

and how solve that ?

Thanks for any suggestions to unblock my situation

hinanotabu86