It's probably your web browser (rather than anything directly related to BT) which is reporting a problem with 'long running scripts'. However it's rarely an actual browser problem that causes the fault; it's more commonly something else on your computer that takes up nearly all of its memory (and/or processing power) and prevents your browser from working properly.
Start by running a full-scan with your anti-virus software, to check that there's nothing found which could be causing the problem. (That's probably unlikely).
A far more likely cause though is some form of malware on your computer (which normal anti-virus programs can't pick up). Download, install and run the free version of Malwarebytes Anti-Malware to see if anything is found (and then zap it via the 'quarantine' option):
https://www.malwarebytes.org/antimalware/
(NB: When installing it, take care to remove the tick alongside the option to take a free trial of the Premium version).
An even more likely cause of the problem though is some legitimate software on your computer hogging all of its resources. Windows updates being installed can cause the problem but a far more frequent cause is your anti-virus program itself (which can cripple a computer while updates are being downloaded and installed). Microsoft Security Essentials and Windows Defender seem to be the worst culprits but I've had similar problems with other security software.
My post on this thread explains how to (try to) work out which program is causing your problem:
http://www.theanswerbank.co.uk/Technology/Computers/Question1425027.html
Once you know what it is you could try uninstalling it and reinstalling it or (better) substituting it with something better.