So you're saying that your PS2client CAN communicate with PS2link on your console, but won't display any messages that were to be displayed by printf()?
How are you launching your PS2client? Is it any different from the say you used to launch it when it still worked?
Somehow I've found that launching it directly from FMCB will cause it to have different results, compared to when it's launched by SwapMagic.
Your console was never changed *before* PS2CLIENT ceased functioning properly, right?
Unmodified SCPH-77006 with SM 3.6
SCPH-39006 with M-chip modchip, SCPH-10281 NA and refurb Seagate 80GB HDD
SCPH-10000 v1.00 with SCPH-10190 PCMCIA NA and SCPH-20400 HDD unit