Error message
xillybus: Incorrect BAR configuration. Aborting.Meaning
This error message indicates that the Xillybus PCIe card's plug-and-play data contains unexpected values. There is by far no reason this should happen, unless the PCIe Xilinx core's configuration has been altered.
Recommended action
Copy the PCIe core's configuration file from the original FPGA kit's bundle, and make changes (if at all) only as necessary. In particular, don't change anything related to the BAR address space.