Can't preview web parts in web parts gallery

I get an "Unknown Error" when I click on any of the web parts in the gall开发者_StackOverflow中文版ery. What can cause this? Thanks, Eric

Some webparts require configuration prior to them working propery. In these cases you need to add the webpart to a page and click the drop down and configure what ever it asks for. The other possibility is that you did not deploy the webpart correctly or you are missing something that it is looking for.