Right now the usual behavior when creating a new JasperReports project is to add in the project build-path the "JasperReports Libraries".
This seems to cause strange issues classpath-related. There should be also a problem of loading twice JR extensions (see bug #2846).
A scenario to reproduce the problem:
1. Create a new JasperReports project beside the usual "MyReports" one already in the workspace.
2. Launch the "New Report File" wizard. Close it.
3. Launch the "New Data Adapter File" wizard.
4. An exception should be raised. See attachment exception01.txt.
5. Removing the "JasperReports Libraries" from the project build-path, and trying to open the wizard again seem to solve the problem.
N.B: Sometimes the exception is not raised.
The problem was initially spotted when replaying the Q7 test cases.
The test case was performing the following actions:
1. Starting from a workspace with "MyReports" project plus another one with the "JasperReport Libraries" in classpath.
2. Opening the "New Data Adapter" wizard from the Repository View.
3. Choosing a JDBC one, and entering the information for a PostgreSQL db.
4. Clicking on the "Test" button caused the exception reported in the exception02.txt file.
As far as I can see, it seems that right now the best solution would to avoid adding the libraries, at least until a full and complete investigation is performed to discover the causes of this issue.
Having the JasperReports Nature should be already enough for a project.