error -63198: system run out of resources when opening multiple FPGA Vi references

I am trying to open 15 of FPGA Vi refenreces using "Open FPGA Vi Reference". Each is connecting to a FPGA card PXI-7842R.  After the PXI real-time system reboots, the program only opens 6 references when it runs the first time, with the rest (9) failed with Error code -63198: system run out of resources. Close a session and retry the operation.

If the program runs the 2nd time, only 5 gets opened and the rest errored out. 4 gets opened at 3rd time. 2 gets opened at the 4th time...... until 0 gets opened at all time.

After I reboots the PXI chassis, it repeated starting with 6 references opened again.

Any idea on what is wrong?

Thanks!

---Ray