Please disable all plugins and test, even the plugins you don't think are the problem. Please make sure they are all disabled at once, not just one at a time because sometimes more than one plugin is to blame.
If this gets better you can start turning on your plugins in small groups. I like to go 4 at a time so I get done 4 times faster and narrow the problem to just the 4 plugins when things break again.
If the problem you are trying to diadnose is with one of the StudioPress plugins you may leave that active to see if the other plugins are conflicting with it.
Once you know which plugin(s) is the problem please contact the plugin developer for support.
If disabeling all plugins does not resolve this please report back with as much information as you can about what happened during this part of the testing.