HELP - PSP 3000 on ARK-5 – New .iso games show as corrupt, but old ones work fine

I have a problem with my PSP 3000 running ARK-5 (latest version). I'm using a SanDisk 128GB microSD card with a adapter.

Here's the issue:

• I have 5 .iso games that work perfectly. No issues at all.
• All of them were downloaded from the same website.
• Now I tried adding a few new .iso games from that exact same site, but the PSP shows them as "corrupted" files. They don't even show the game icon.
• I've also tried downloading games from other websites – same problem. They all show as corrupted.

What I've tried so far:

• Checked the file extensions – they are all .iso
• Made sure the files aren't in .rar or .zip format
• Placed them in the ISO folder on the root of the memory card
• The card is formatted as FAT32 (since I use a 128GB card)
• Tried different download sources (multiple websites)

The old .iso games still work perfectly. Only the new ones (from any source) show as corrupted.

Has anyone else experienced this? Could it be a problem with ARK-5, the SD card, or something else? Any help would be appreciated.

Thanks!