Cannot convert str to pysph.base.nnps_base.DomainManager

[DaYongUpUp]

I construct a solver in a class, and call run in a function, however I run into an exception like this:

Exception has occurred: TypeError
Cannot convert str to pysph.base.nnps_base.DomainManager
File "D:\Projects\Codes\PySpheral\src\pthreads.py", line 17, in run
self._solver.run()

please can anybody help with that?