Carbon cache not starting

I am getting following Errir message when i start my carbon cache:
/opt/graphite/bin$ ./carbon-cache.py start

Error Message:
Starting carbon-cache (instance a)
Traceback (most recent call last):
  File "./carbon-cache.py", line 30, in <module>
    run_twistd_plugin(__file__)
  File "/opt/graphite/lib/carbon/util.py", line 92, in run_twistd_plugin
    runApp(config)
  File "/usr/local/lib/python2.7/dist-packages/Twisted-11.0.0-py2.7-linux-i686.egg/twisted/scripts/twistd.py", line 23, in runApp
    _SomeApplicationRunner(config).run()
  File "/usr/local/lib/python2.7/dist-packages/Twisted-11.0.0-py2.7-linux-i686.egg/twisted/application/app.py", line 376, in run
    self.application = self.createOrGetApplication()
  File "/usr/local/lib/python2.7/dist-packages/Twisted-11.0.0-py2.7-linux-i686.egg/twisted/application/app.py", line 436, in createOrGetApplication
    ser = plg.makeService(self.config.subOptions)
  File "/opt/graphite/lib/twisted/plugins/carbon_cache_plugin.py", line 21, in makeService
    return service.createCacheService(options)
  File "/opt/graphite/lib/carbon/service.py", line 127, in createCacheService
    from carbon.writer import WriterService
  File "/opt/graphite/lib/carbon/writer.py", line 34, in <module>
    schemas = loadStorageSchemas()
  File "/opt/graphite/lib/carbon/storage.py", line 129, in loadStorageSchemas
    mySchema = PatternSchema(section, pattern, archives)
  File "/opt/graphite/lib/carbon/storage.py", line 55, in __init__
    self.regex = re.compile(pattern)
  File "/usr/lib/python2.7/re.py", line 190, in compile
    return _compile(pattern, flags)
  File "/usr/lib/python2.7/re.py", line 242, in _compile
    raise error, v # invalid expression
sre_constants.error: nothing to repeat

my storage-schemas.conf :
[server_load]
priority = 100
pattern = *.
retentions = 1m:7d

please help me to resolve this issue.

Thanks