The QCP export/import process that HP created really should only be used for smaller projects. If you get the above error, you can still try to restore the project, as long as both the database and repository FULLY imported (which is difficult to verify). In this instance, you just need to delete the record of the project from the PROJECTS table in the qcsiteadmin_db database and Restore pointing to the dbid.xml.
Below are the limitations of QCP file exporting/archiving. Anything bigger and you will want to instead take direct backup copies of the project's database and repository.
*There is a technical limitations in place caused by the dependency of the process on zlib and jzlib technologies. These technologies are used by QC but are not part of the source code and cannot be changed:*
*1) The project including repository and database should not exceed 4 GB*
*2) The QCP file should not exceed 2 GB*