This is expected. You cannot run/import 2.6 .pyc files in python 2.7 because the file format has changed.

$ echo 'print "hello"' > tmp.py 
$ python2.6 -c 'import tmp'
hello
$ rm tmp.py
$ python2.7 -c 'import tmp'
Traceback (most recent call last):
  File "<string>", line 1, in <module>
ImportError: Bad magic number in tmp.pyc

Naval, if you do have the source xxxx.py make sure that you delete all occurrences of xxxx.pyc in directories preceding the directory containing xxxx.py in sys.path. Sometimes this error is the result of moving a .py file into another directory and forgetting to delete the leftover .pyc.