To avoid abuse of the system, Instagram imposes certain limits on third-party services and apps, in particular the amount of likes, follows, unfollows and comments that you can do in a short period of time.
Usually the block lifts after an hour at most, but the more you are blocked the longer it can take. If you have been blocked many times then your account will be flagged and it could be a few days until you are able to continue as normal.
In most cases, this can be resolved by logging into the official Instagram app on your mobile device, changing your password and entering a verified email address and phone number in your Instagram account details.
Another possibility is that you have reached the maximum number of follows allowed by Instagram, which appears to be +-6000 in a 30 day period at this stage, but can change at any time.
If you have tried everything and you are still blocked, then please remember you are being blocked by Instagram itself and it is completely out of our hands. Your only option is to wait it out. Giving your account a complete break for a few days may speed things up and result in the block being lifted sooner.
As with all similar software, you need to stay under the radar to avoid being flagged for spamming. Try keeping your total follows, likes, etc. under a few hundred per day. Using a decent time delay setting is also crucial. You may be able to get away with less, but at least 1 minute is recommended to be safe.