Dwhonan posted in our forums that he was having trouble installing the Enhanced Gmail Plugin. He got the classic 907 Invalid COD error while trying to install the application wirelessly. I just assumed he had some issues with his device/OS but Johnny reminded me of a article RIM published back in 2008 that lists the top 10 reasons for getting a Invalid COD or Invalid Jar error during a wireless OTA installation.
Many of the solutions or workarounds require you to be the developer or have access to the server but still it is a great read. Check it out at this link. Its also good to know that there are quite a few other causes for this issue like the one experienced by Documents To Go users. (Credit goes to DataViz for the images)