can't save openERP report designer

hello i want to customize the reports in openerp and for that i installed base_report_designer and report_designer modules and then a screen comes to save the openerp report designer. but when i press the save as button the following error occurs

File not found
Firefox can't find the file at http://localhost:8080/openerp/form/save ... p_id=False.
Check the file name for capitalization or other typing errors.
Check to see if the file was moved, renamed or deleted.

and another error appears at the terminal:
[2012-03-10 15:04:29,760][db] ERROR:web-services:Uncaught exception
Traceback (most recent call last):
File "/home/pravitha/workspace/openERP/src/openerp-server/bin/osv/osv.py", line 122, in wrapper
return f(self, dbname, *args, **kwargs)
File "/home/pravitha/workspace/openERP/src/openerp-server/bin/osv/osv.py", line 176, in execute
res = self.execute_cr(cr, uid, obj, method, *args, **kw)
File "/home/pravitha/workspace/openERP/src/openerp-server/bin/osv/osv.py", line 164, in execute_cr
object = pooler.get_pool(cr.dbname).get(obj)
File "/home/pravitha/workspace/openERP/src/openerp-server/bin/osv/osv.py", line 250, in get
obj = self.obj_pool.get(name, None)
TypeError: unhashable type: 'list'

can anyone help?////please

_________________
Regards,
Nightfury