You're building within the spawn-protection area, so only ops can affect blocks (including levers and doors) within the range of the protection.
To fix this you can pull up stakes and move away from the spawn, rebuilding elsewhere. That might be a lot of work, though, so alternatively you can reduce the size of the spawn's protection radius in the server's configuration file. On an FTB server (which uses Forge, which changes the config options for spawn protection compared to the vanilla server), you want to look for or add this line:
(That line is from my own server on which I've increased the protection area. The default is smaller; 40, I believe.)
Once you find the line, reduce it down as necessary until the stuff you want accessible to your players can be used by non-ops. (To test this, I find it's convenient to de-op myself and work outward from the spawn centre until I find blocks I can break, then re-op myself using the server console.)
Yet another alternative is to disable spawn protection entirely by setting this line to
Shrinking or disabling spawn protection is only recommended on private servers where you trust your players, of course!