Sometimes our link checker gives "false positives" - i.e., reports that a link is broken even though it's working fine.
Sometimes this is because the link didn't work at the time it did the check but subsequently is working again - a temporary failure of the linked website.
Other times it's because the web server is blocking our link checker because it's detected that it's not a "human" visitor. In this case the checker will get an error back from the site, but when you visit it it works OK.
So, if you've manually checked the link and it's fine then you can probably just ignore the warning about the broken links.
If you want me to look at it more closely please confirm the details of the page/link that are being reported and I'll see if I can sort it out.