Unexpected "PS Disk Door is Open" when playing PSX ISO using multiMAN.

It is strange for me to get "PS Disk Door is Open" when playing a PSX ISO using the latest multiMAN. The "PS Disk Door is Open" icon shows up then disappear after a few seconds then not at all for some periods of time.

My PSX ISOs are on an external hdd and everything is properly connected to my PS3. I'm differentiating between what the problems may be but still haven't found a solution on my own.

Any Ideas?