[MacNNUK]

I did have an apple wireless mouse installed 2 years ago, but removed it soon after because it was interfering with my wireless CCTV cameras.

I normally keep bluetooth turned off by default.

Occasionally now, from startup, and before I get to the main screen I get a very large error message, in a whiteish block saying bluetooth mouse not found, and my bluetooth has been turned on, as shown by my top menu icon.

It does not recognise my cabled mouse, through the keyboard.

Nor the keyboard.

I have to physically restart with power switch to remove the message, and reload

I then, yet again, turn bluetooth off.

The iMac then behaves normally for a few days


Any ideas why this is ?

[P]

Most likely the bluetooth thing is a secondary effect. Your problem is that the mouse is not detected, which makes the Mac remember that it once had a bluetooth mouse attached and start asking for it.

[Waragainstsleep]

OS X will look for bluetooth keyboard and mouse if it doesn't detect USB ones. Whether you had one in the past or not has nothing to do with it.

[MacNNUK]

Originally Posted by Waragainstsleep 

OS X will look for bluetooth keyboard and mouse if it doesn't detect USB ones. Whether you had one in the past or not has nothing to do with it.

That could tie in with my USB keyboard and mouse freezing after sleep sometimes.

[Waragainstsleep]

When the keyboard freezes, unplugging/replugging doesn't help?
Can you screenshare in from another Mac?
You might find a clue in your system logs.