What is the model number of the PS2 that was used to install FMCB? If you did not make a multi-install of FMCB v1.8C, your FMCB installation is region-locked. Older versions of FMCB are region-locked.
All Playstation 2 consoles have model numbers in this format: SCPH-XXXRR, where RR is the region number.
The only Playstation 2 models that can share a FMCB installation will be those region 03 and region 04 models.
SCPH-10000 S. MINOKAMO v1.01 (Defunct)
SCPH-10000 S. KISARAZU v1.00 (faulty)
SCPH-15000 S. KOHDA (With warranty seal!) :D
DESR-5100 S. EMCS