Customer Search is not working

Really need some help. I'm running CustomerSearchBasic in sandbox environment. I have two pieces of code
1.         CustomerSearchBasic customerSrch = new CustomerSearchBasic();
       
        SearchResult srchRslt = null;
        while (!operationSuccess) {
            try {
                // Invoke the "search" web service
                srchRslt = nsPort.search(customerSrch);
                operationSuccess = true;
                if (srchRslt.getStatus().isIsSuccess()) {

2. Similar code but searching for specific external id, which works fine.

First piece of code never goes through and at the end I get {urn:faults_2008_2.platform.webservices.netsuite.com}exceededRequestLimitFault:<platformFaults:code>WS_CONCUR_SESSION_DISALLWD</platformFaults:code><platformFaults:message>Only one request may be made against a session at a time</platformFaults:message>