These ports don't go bad nearly as often as, say, a NES port might, but they're still prone to errors. Typically problems will occur after a long period of disuse. Happily the fix is usually quite simple.

Slap a few layers of scotch tape under your HuCard, under the pins, ensuring that no tape extends past the sides of the card. This will apply more pressure on the pins inside. Now insert the HuCard into the system and pull it out a dozen times or so. This creates a kind of scrubbing action where the card itself scrapes off any oxidization on the pins inside. There's a little lip on the front of most HuCards that does a great scraping job.