Folder could not be displayed in OE

Greetings,

When open my outlook express 6.0 it shows

“Folder could not be displayed”

Outlook Express could not open this folder.
Possible causes are:
Low disk space.
Low memory.

I check my disk space still available and I try go tomaintenance folder to clean up and compact the local file, this error message still presist, can anyone help me to solve this problem. Thx