Can anyone tell me why I am getting a NULL value for the nodata function..... I'm using the nodata function so I never get a NULL..... 
20228:20091207:104144 Expression [{141323}=1] for item [111206][ocsprddb1.ctc.trb:agent.ping] cannot be evaluated: unable to get function value: lastvalue IS NULL for function [141323][ocsprddb1.ctc.trb:agent.ping.nodata(21600)]
Is there a maximum time I can specify for the nodata?

20228:20091207:104144 Expression [{141323}=1] for item [111206][ocsprddb1.ctc.trb:agent.ping] cannot be evaluated: unable to get function value: lastvalue IS NULL for function [141323][ocsprddb1.ctc.trb:agent.ping.nodata(21600)]
Is there a maximum time I can specify for the nodata?