Two days ago I tried to put some ads on this site. As the first step of this process you have to validate your site by AdSense.
For my surprise, after some hours the validation failed with a policy violation message. The feedback was too general, I had no clue what was wrong with my site. I've altered a lot of things, but the second validation failed again.
I tried to check the issues to fix in the AdSense Policy center, but as I opened the page, I got the following message:
We apologize for the inconvenience, but we are unable to process your request at this time. Our engineers have been notified of this problem and will work to resolve it.
After patiently waiting for two days it turned out this was not an AdSense error, their engineers didn't worked to resolve this at all, they most likely weren't notified at all and I could have waited till the end of time to get this sorted out by Google.
It was the AdBlocker which has prevented some AdSense pages to load properly.
So to recap: the solution to fix the "We apologize for the inconvenience..." error is to turn AdBlocker off.
I hope this helped and you hadn't waited too long in vain for the AdSense engineers to resolve this issue.