Google Tag Manager issue

Hi, just got into trouble when installing GTM code for my website. Previously, I’ve installed it on a Wbeblow project and it worked just fine, but not this time.
As always I’ve put the first part of code into Head Code section and second into Footer Code section.
After installation Google Tag Manager Assistant shows 2 issues.
1 says “An error occured while the tag was fired: net::ERR_ABORTED”
2 says “Error while sending request: net::ERR_ABORTED”

I’ve reinstalled it a few times, but the problem remains. GTM is damn important for analytics/goals and remarketing purposes, so I can’t just skip it.
Can anyone suggest me how to deal with it?