Question: Just by a mistake I had deleted a spring project in STS.To use it back I borrowed the same project from my friend in zip format but when I tried to import it says

*Some projects cannot be imported because they already exist in the workspace*

Following is the way I tried to import

file->import->general->existing projects into worspace->select archive file

and after browse when I select the zip project 

*Some projects cannot be imported because they already exist in the workspace*

and the finish button and next button are in disabled state.Please help me

Answer: 
Generally this kind of problems not occurred you can go to Project option and clean and than restart STS.
May be STS is not synched with the latest configured project.
the problem is that when you delete a project maybe sts only close it.
Try View Menu --> uncheck closed projects
Now you will see all closed project, simply delete it.