From FP 1000 User Manual, page 34,
The FP-1000/1001 has detected an error in the
terminal bases in the bank or has identified a module in
an illegal state. Verify that the protective cover is on the
local bus connector of the last terminal base and that
none of the pins of that connector are touching or bent.
The manual is at the URL
http://www.ni.com/pdf/manuals/370706a.pdf
Hope it helps!
Graziano