as mentioned in my forum thread (ID: 2947177), there are encoding issues in the communication streams between aspell and texlipse. This occurs if the system's (or java's ?) standard encoding differs from the encoding you use in your latex files.
To fix the issue, initialize both input and output streams of the aspell process communication with the same encoding used in the file you want to spell check. The attached patch does the job and can be applied via the team->apply patch... option from the eclipse context menu of the project.