An error occurred when searching; 'Exchange Web Service call for keywords statistics information failed. Error: Invalid search query syntax or the query contains invalid search properties.'

i am trying to perform a discovery search in exchange 2010 cross premises environment.

The message is 'Exchange Web Service call for keywords statistics information failed. Error: Invalid search query syntax or the query contains invalid search properties.'.

any idea about this and why this is happening and wat will be the cause of this