I agree with Ken. This is why I said you can't just go by every computer having Cat6.
Try this, which likely won't help, but it will give you info.
Go C:\Program Files (x86)\Amazing Charts or wherever your program actually is on a given computer. (Not the server).
Right click on Amazing Utilities.exe. Choose Run as Administrator. Select "Advanced Options" then "Test speed from database."
You may want to do this as you add AC programs.
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Go to Control Panel -> System -> Device Manager -> Left click on your NIC card
Then choose Link Speed in the tabs. This should show you your Link Status, e.g. should say 1.0Gbps/Full Duplex.
Under Speed and Duplex, it should say Auto Negotiation.
Check on each computer. If it is less than 1Gbps, then check Speed and Duplex. If it says Auto Negotiation (which is best), you may want to change to 1Gbps Full Duplex in the drop down.
MAKE SURE THAT ALL OF THIS IS CORRECT ON YOUR MAIN COMPUTER. IF IT IS SOMETHING LIKE 10Mbps or even 100Mbps, that would be a problem. Actually, 100 shouldn't, but you still want the 1Gbps.
If off on any computer, it could be the setting or problem with Auto Negotiation or the card may not be rated for 1Gbps.
I know your IT person said everything was clear, but, I would check all these things I mentioned and what Ken mentioned.
Make a list of all computers with the main computer on top. Write down all of these troubleshooting steps on a table. Then check them such as
Nurse computer: 0.677 for speed to database | NIC 1Gbps etc.
MAKE SURE YOUR SWITCH IS A 1Gbps switch.
I would think that if a computer were running at 10Mbps, it would be slow even if none of the other computers were running AC.
As stated before, some offices make sure every computer is either Logged Off or turned off. But, you can just lock your computers allowing AC to always be on. Not sure if it is a problem starting them up or just if they are all on.
This shouldn't be a difficult problem to troubleshoot given the way you can reproduce it. For me, it is bandwidth on the network as you continue to have to run more data to and from the server as you add computers. If you only have, let's say, 10Mbps on the server computer, one can do fine, but two is then a problem, three is worse.
