There could be a few reasons for this: 

1. Depending on where you posted it, your thread may need approving first, in this case you will be notified in due course. Please be patient as the moderators are very busy.

2. Your post or thread has been deleted due to a rule violation. Terms and Conditions    
3. It's a known error that's being worked on, after awhile it will go away. If problem persists, contact admin.