Unexpected meta character at xsd pattern

I have a pattern in an xsd file to check a json value in an xml file is valid for my system. I am getting an unexpected meta character error when i run the validation stage. I checked meta characters but, i couldn't see the meta character that causes error. Any idea what is wrong?

NOTE : in original pattern i use " for "

So here my regex :

\{(\s*"*[a-z]+"\s*:\s*"[^"]*("\s*,)?)*"\s*\}