The phrase 'not able to access' is correct and usable in written English.
You can use it when you are referring to being unable to obtain something or use something. For example: I was not able to access the documents I needed to finish my project.
"We're seeing reports that some users are not able to access YouTube in Turkey.
Predictably, mainland Chinese users are not able to access the site easily.
Customers of Icesave bank in Britain, controlled by Landsbanki, were not able to access their money on Tuesday.
The company's online fashion show in February 1999 attracted such a swarm of visitors that some users were not able to access the site at the time.
Prisoners are often not able to access courses and support without first admitting guilt, something miscarriage of justice victims cannot and will not do.
He endured a period of enforced limbo as asylum seekers are not allowed to work and are not able to access many educational opportunities or any mainstream benefits.
Between roughly 9pm and 11pm on 6 March customers were not able to access online banking, and also had problems using ATMs and "point of service" payments.
It is not able to sell its oil unencumbered and when it does it is not able to access the proceeds of its sale freely".
It is understood that around 600,000 customers were not able to access their accounts properly, with many still waiting for credits to appear.
People who were curious about the new channel but were not able to access it on TV found that they could not access it online, either.
Local residents were not able to access YouTube at all; however, access to Facebook was not uniformly blocked across the valley.
