In situations where a keyword query is issued which includes a large number of property restrictions, Search Server may issue an error indicating that the query is malformed.
Upon executing a keyword query (using the Ektron search API with the 'KeywordSearchCriteria' input) an error occurs indicating that the query is malformed. This symptom typically presents itself with keyword queriesthat exceed 10 individual property restrictions.Search Server places restrictions on the keyword queries that it will accept for execution. When a query's length or complexity exceeds Search Server's internal limitations, it returns an error indicatingthat the query is malformed.The Ektron search API provides support for both of the query languages supported within Search Server. When a query is issued from the CMS with the 'KeywordSearchCriteria', it is transformed to Search Server's keyword querysyntax. When a query is issued from the CMS with the 'AdvancedSearchCriteria', it is transformed to Search Server's full-text SQL query syntax. In situations where you find the complexity of your query exceeding the limitations of the keyword query syntax,apply the the 'AdvancedSearchCriteria' instead.MSDN:Keyword Query Syntax Reference