Even though Dish’s Sling TV streaming service had two full months of active, national usage under its belt — and even though the company says it expected high demand during the Final Four of the NCAA Men’s Basketball tournament — some Sling users were left staring at error messages instead of watching the end of Kentucky’s almost-perfect season. And with HBO expected to launch both its standalone streaming HBO Now service and live access via Sling this week, there’s cause for concern.

Re/code points to numerous complaints over the weekend about error messages on Sling, which had been actively touting that users could watch Final Four games on the Turner channels included in the $20/month core package of Sling.

“We’re sorry some basketball fans saw errors tonight due to extreme sign-ups and streaming,” reads a Tweet posted Saturday evening by the @SlingAnswers account. “Engineers rebalanced load across network partners.”

Dish contends that the errors only affected a “fraction” of Sling users, but the service’s failure to meet full demand for such a high-profile event raises concerns about streaming video during a landmark week for the technology.

HBO is expected to launch its standalone streaming service HBO Now this week in advance of the April 12 season premiere of Game of Thrones. At the same time, it’s also announced that Sling will be selling both live and on-demand access to HBO for $15/month.

HBO Go, the network’s streaming service for customers who subscribe through traditional pay-TV vendors, has historically shown its inability to cope with high demand during season premieres, and most notably during the first season finale of True Detective in 2014.

HBO Now has been developed with an outside partner, MLB Advanced Media, the baseball folks responsible for the MLB.tv streaming service, which — unless today is different from the previous decade of opening days — will have its hands full dealing with the inevitable huge number of complaints today as users try to watch their still-undefeated favorite teams online.

Then there’s last week’s announcement from Sling that it will carry HBO and that it will launch the premium network in time for the GoT premiere.

Given HBO Now’s initial exclusivity on Apple TV and iOS devices, a number of people will choose Sling both because it’s available on more devices and its HBO access will be live.

But if users see a repeat of Sling’s Final Four faltering, or any of the HBO streaming options crash like HBO Go has done in the past, the people involved should expect a very vocal backlash from paying customers (and the friends who borrowed their passwords).

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