This message has the following cause and solution:
You have tried to share a file that has the same name property as one in the target project.
There are several possible causes for this message. If you did not assign the Name property in one of your files, you could be conflicting with a file in the target project (where the Name property also was not assigned or is identical). In this case, assign the Name property of the file in your current project, and then try again.
Other possibilities are that the project file is checked out to someone else, or you were not able to check out the project file. Check the file's check-out status to determine if this is the case. Or, there could have been a Visual SourceSafe internal error.