Without going into too much detail at this stage, we are having problems with 'freezing' when several users save back to the network at the same time. It doesn't always happen, but often enough to be a pain.
Thing is, the exact same laptops with the exact same image are being used in another area, and they are not having the same problem. Neither the edge nor core switches show any errors, nor does the wi-fi controller (which has current firmware). Fibre cabling is new and clean and tested OK. So nothing concrete points to the laptops, switch or controller or cabling, and it's not software either because laptops in both areas share the same msi and prism packages. Nothing sits between the AP and the clients, so I don't think environment is the issue, either. I know it has to be one of the above, but there are no clues.
I am going to try swapping out the AP, the POE injector being used for that AP, the fibre gig module and the switch as well if I get that far (all in separate stages of course), but I was just wondering if anyone had experienced something similar and had resolved the problem.
You need to rule out non-wifi interference and co-channel interference. Non-wifi Interference requires a spectrum analyser, check out metageek's Wi-Spy it's $99-$599 depending on how many features you want but it's well worth the investment to track down interference. In the absence of a spectrum analyser try changing the channel that the access point is running on in the problem area. Finally using something like InSSIDer or NetStumbler do a scan in the problem area and make sure APs are using non-overlapping channels 1, 6 and 11 and make sure you can't see more than 2-3 APs on the same channel from that location.
You didn't detail what your setup is, but I've seen this before although in a far worse case where the wifi adapter on the device (laptop in this case) floods the RF channel and stops anyone accessing the network, the foolproof approach is to use laptops/wireless with a/b/g/n ranges.
Are they all on the same model device? if not are there more of one type of model than the other, it might only be one of the devices which is causing the problem for the other users. As Paul above has said you won't really know without some type of analysis.