I connected my existing external HDD (@USB2.0) to a new PC with Win 8.1. From the beginning all partitions mounted properly and were accessible as expected but later suddenly the first partition was not accessible due to insufficiant access rights. All other partitions keep being accessible except this one. I wonder how this could happen, especially when it's a FAT32 format partition (no eser-level security support) The exact errors I'm receiving are these:

Currently you don't have permissions to access this folder.
For obtaining permanent access to this folder,click on the option Continue.

If I click Continue I get this warning:

Permission to access this folder was denied.
For obtaining access to this folder, you'll have to use security tab.

If I click the Security tab link, I get properties dialog for that partition opened, however no Security tab is available (oviously, this is a FAT32 volume)

I would appreciate an soulution how to reenable access to this drive.