SNES-Station never officially supported loading from another device than CDVD.
Those versions which do, have this support 'hacked/patched into them' and those versions are not as stable as the original build...
Which version have you even used?
USBv1, v2, HDD, or ffgrievers version?
PS2 V7/DMS3 V2 (FW:2.4b7); Seagate Baracuda 200GB
PS2 V7/CC1.0 (FW:34 hacked v2 BM:2.1.6); Maxtor DiamondMAX9 PLUS 160GB
PS2 SCPH-30004R; NoMod+NoLaser
3xSony MC 8MB
MAX/Datel 16MB with Boot-CD
Custom FMCB 1.8b+ Beta-Build, my AIO 0.5, Sony&xRhino-Linux