I'm following the "Custom Messages" tutorial on the Gazebo tutorials website. When I try to launch gazebo with a custom world that includes my plugin, I get the following cryptic error message:

aes048076:build glenhenshaw$ gazebo -u ../worlds/allegrodog.world
[libprotobuf ERROR google/protobuf/descriptor_database.cc:57] File already exists in database: altimeter.proto
[libprotobuf FATAL google/protobuf/descriptor.cc:1272] CHECK failed: generated_database_>Add(encoded_file_descriptor, size): 
libc++abi.dylib: terminating with uncaught exception of type google::protobuf::FatalException: CHECK failed: generated_database_->Add(encoded_file_descriptor, size): 

Some googling of this error seems to indicate that somehow I've inadvertently linked two copies of the protobuf library into my plugin, or I've linked in two copies of "altimeter.pb.cc".

I don't use "altimeter.pb.cc" anywhere that I can see. I certainly don't use it explicitly. And the linking is all being managed by cmake, as per the tutorial instructions.

Any help would be appreciated here, I've been beating my head against this for three days now...