I didn't even know you could claim a certain radius? Well goes to show you learn something new everyday.
This is not a bug, you are trying to claim more land than you have power. The factions plugin does not allow this.
You said it was likely. I'm saying it for sure, as I believe a radius of 3 would be 49 chunks of land (a 7x7 square) A radius of 1 is just the chunk you're in. A radius of 2 is the chunk your in plus an extra chunk in all directions. (a 3x3 square) A radius of 3 is the chunk you're in plus 2 chunks in each direction. (A 7x7 square) I doubt they have the 50 or so power needed to claim a radius of 3.
I didn't realize that the issue was so basic.... I never have any power issues, so I rarely consider power
Yeah, it will tell you that you cannot claim land from <land owner> if you are at your land claims equal your power.
As Jess said its probably not a glitch or problem, it is probably a power problem just maybe recruit some new members or unclaimed some land.