I found an exact match .net domain for a keyword that had 6000 "exact search matches" per month. Was not something great but seemed a decent try. I took a coffee break and suddenly noticed that I was not able to register the domain via hostgator, things were just getting hung. Then I tried bluehost, same result there, the page was just not opening for me. Even after an hour same situation , but I found through domain suggestions that the domain was still available. But alas I was unable to get through to the registration page on both my favorite hosts. Another 5 min go by and I notice that the domain got registered just few minutes back. Now I tried opening bluehost and hostgator and viola, they both opened super quick. It was almost like I was blocked till the domain was registered. STRANGE is the word!
Try to register the same domain name using another domain name registrar. Ask them for help in understading this issue. I have heard some not honest domain name registrars or resellers can taste your domain name.
have you looked the whois once ? some times domain suggestion softwares wont check availability of all domains