Keychain problem with encrypted hard drive

Hi,

I have an external Hard Drive encrypted with Disk Utility with its password stored in Keychain.

Sometimes when the drive is mounting keychain asks for its password but does not accept the correct password when I enter it. If I hit cancel the drive is mounted anyway without the password.

Keychain First Aid does not detect any problems. The issue repeats every time the computer is booted and the drive mounted, until I delete the drive from the Keychain Access login list. This solves the problem for a few days but then the issue appears again. Drive asks for password - password not accepted but drive mounted anyway.

Has anyone else encountered this problem?

Thank you!