error on saving a new task

When i try to save a new task with remaining time and work done. (Last revision)
I got this message:
raceback (most recent call last):
  File "/home/phil/trunk/server/bin/netsvc.py", line 223, in dispatch
    result = LocalService(service_name)(method, *params)
  File "/home/phil/trunk/server/bin/netsvc.py", line 74, in __call__
    return getattr(self, method)(*params)
  File "/home/phil/trunk/server/bin/service/web_services.py", line 430, in execute
    res = service.execute(db, uid, object, method, *args)
  File "/home/phil/trunk/server/bin/osv/osv.py", line 59, in wrapper
    return f(self, dbname, *args, **kwargs)
  File "/home/phil/trunk/server/bin/osv/osv.py", line 119, in execute
    res = pool.execute_cr(cr, uid, obj, method, *args, **kw)
  File "/home/phil/trunk/server/bin/osv/osv.py", line 111, in execute_cr
    return getattr(object, method)(cr, uid, *args, **kw)
  File "/home/phil/trunk/server/bin/osv/orm.py", line 2212, in write
    self._columns[field].set(cr, self, id, field, vals[field], user, context=context)
  File "/home/phil/trunk/server/bin/osv/fields.py", line 434, in set
    obj.create(cr, user, act[2], context=context)
  File "/home/phil/trunk/server/bin/addons/project_timesheet/project_timesheet.py", line 58, in create
    vals_line['name']=obj_task.name + ': ' + vals['name']
TypeError: coercing to Unicode: need string or buffer, bool found