I had a situation in which one of my configuration parameters in a TeamCity build did not have a name or a value. Because it was supposedly used by one of my build steps I couldn’t delete it. Because it didn’t have a name or value I couldn’t run the build. I tried editing the value, but the name is uneditable.
The answer is that I had a double-% character on one of my build steps. TeamCity uses the % character as a flag to indicate a configuration parameter. I had %PARAMETER%%. in one of the build step fields. All I had to do is change it to %PARAMETER% and everything was fine.