Basically this means that Twitter does not like links in your posts. In most cases Twitter just does not allow posts with links to your website/domain/server/IP/etc.. In some cases Twitter rejects the content of your posts.
For example links to any site hosted with free hosting provider are permanently banned on Facebook and Twitter. Too many people tried to setup the sites there for the purpose of spam.
Please contact Twitter directly if you have questions or concerns about that issue.