Every once in a while, especially when you’re in the testing phase, you can deploy a solution with a feature, web part, etc. and, instead of seeing ‘Deployed’ in the Status column, you see a red-colored ‘Error’. At first, you might be baffled, but it’s fairly easy to untangle the mess you are perceiving.

When you’re in the Solution Management page, just click on the link for your solution, which will take you to the Solution Properties page. Any errors which were detected should be listed there on the page, along with possible fixes.