It depends on the size of the XML file you are trying to upload. We found that there are size limitations that can cause issues. I would recommend contacting CompuWare (Micro Focus) support for assistance with this issue. They can either resolve the issue or find a workaround for you.
ElMojito: Please remember that this is an international professional forum that includes many people that do not speak english or older folks that do not understand texting. So that your posts can be understood (and translated properly), please type out each word fully. This is listed in the guidelines and rules for using SQA Forums. Thank you.
Size is definately a consideration, but if your not importing a large file and still experiencing an issue you should contact tech-support. I recall there being an issue in either 6.0 or 6.1 where some assets could not be imported. I believe it had something to do with importing to a project other than Common. This problem should be resolved in a patch.