PCSX2 now uses 8MB memory card files by default . If a save is from a 64MB card, you may need to create a 64MB card in the emulator first.
"Because people forget," Lena said. "And because some memory needs witnesses." Downloads - PS2 Memory Card Save Files -Emulator- - The Tech
Before Lena left the house that afternoon, she handed Kai a new file—named simply WITNESS_BACKUP_SLOT1.psu. "Keep it," she said. "If you ever find another, don't upload it. People don't go looking for witnesses. They need them." PCSX2 now uses 8MB memory card files by default
However, using a downloaded save to cheat in online games (via emulated LAN services like XLink Kai) is often considered unethical by communities. Always use downloaded saves for single-player enjoyment or recovery, not disruption. Downloads - PS2 Memory Card Save Files -Emulator- - The Tech