Rick -- it worked, thank you. I needed to install R288120 which is the driver for the Dell 375 adapter. Everything now works beautifully. Thanks for your pateinec and dedication while I fumbled my way through. Got there in the end! 
I have just added an internal Dell bluetooth adapter (to avoid having to use a USB device) to my company supplied Dell Latitude E6420. (BT adapted was not specified as an option, unfortunately). All seemed well expect that when pairing a device (say BlackBerry or TV), the device appears momentarily as being attached, this disappears again. I strongly suspect that as well as installing the physical adapter, I also need to add a suitable driver. Problem is: which driver do I need? (oh... and how?) The BT adapter was provided via the Dell website and came in a Dell box. (I had to buy the small ribbon connector too). Any hints, tips would be appreciated: I have trawled through countless items in an attempt at self help, but having failed to find anything much more than the standard driver update sites, I am now hoping that someone out there with can give me some good advice. Hoping this is in the right forum... Thanks in anticipation...    
Bluetooth adapter self installation/upgrade not fully functional 