DeleteOperationImplementation error

I've finallly find the problem.

My project used the .properties file to store some attributes of the project like last date/time was modified, name, .... and when a project was loaded, it creates a Properties object that I put in its lookup.

This Properties object has locked the .properties file.
Now I use the ProjectInformation object to store this data, and I have not the problem deleting projects.

Thanks for the answers.