I live in California and I have applied for removal of conditions of residence (I 751) on dec 08. They called us for an interview on July 13, 09. I was on Monday at 7am. We were the only couple there. The officer gave us a hard time making questions, trying to intimidate us. We were pretty confident and we brought lots of photos and documents. After 15 min of interview, the office said that the computer system was out and he couldn't do the SECURITY CHECK on me. He said that we could go home and, as soon as the system comes back he would do the security check and if I get approved, he will send us the approval notice. I want to know if this is something that usually can happen and how long should I be waiting for this approval letter?

Nothing unusual for a delay for security clearance.

In the vast majority of cases, it is relatively short but in extreme circumstances, very long. If you don't hear from them in 30 days, do a status inquiry. Probably best to schedule an INFOpass appointment to check.

Usually the second SECURITY CHECK is faster than the 1 st one because they only check from the time of the 1 st one till the second one. And when you apply for your naturalization it will be from the second till the time you applied. Bottom line ,if the 1 st one was fast the other 2 should be faster