While television viewers in Scotland could watch the clash between the country's First Minister Alex Salmond and former Chancellor Alistair Darling, a surge in demand online across the rest of the UK caused STV's livestream to crash.
On Twitter, STV said: "For those having problems with the STV Player at the moment we are aware of this and are working hard to fix it."
Later it added: "We're still working on fixing the live stream. The debate will be available online in full a few hours after the programme has finished."
A number of viewers expressed their frustration on Twitter.
Labour MP Diane Abbott wrote: "Finally watching #indyref debate after struggling for 40 minutes with dead STV Iplayer."
Broadcaster Andrew Neil added: "Trying to watch Salmond v Darling on STV iPlayer. But system seem overwhelmed. Any thoughts?"
Claire Stewart tweeted: "An independent Scotland needs better equipped public broadcasters. #stvcrash #ScotDecides."
Labour MP Tom Watson said: "It may not be of interest to many but you would have thought a debate on the future of the union would be broadcast UK wide."