Has anyone had a problem that all of a sudden the uno is no longer recognized? I have six uno's and only one gets its scetch and runs fine. I am pulling 1 uno out of cable and plugging next in. Get the same error message Unos with sketches installed a few weeks ago and running fine, just arnt excepting new sketches. " problem uploadigto board" Am I rambling?
Yes a little rambling 
It is ok to space your text and add extra detail such as the version of the IDE and if they are real or clone UNO's etc etc.
To fill in some of the etc etc
Boards recognised by OS?
Error messages.
Etc etc
Some clones some real deal. All R3
Ide is latest verson downloaded yesterday, sorry not at my computer.
Bought a 5 pack of nanos, clones and can't get any of those to work.. And yes switched to nano board..
This has a feel of I am just doing something wrong..
NANO clones could be either of 328P or 328P (old bootloader) when you select the "Flavour" of board.
Some clones require a driver that may not be included in the IDE CH340/341 or CP2012
Not sure why UNO would give you the error though unless it may also be a driver issue ?
For whatever the reason... When I took a uno out and put another in the port changed, never happen before. But suddenly I have a bunch of working audrinos