WHERE clause statement?

[RedDucati748]

My question relates to the WHERE clause in my SQL statement. I ran the query with a single condition, which is shown in the SQL below. When a second condition is added to the SQL statement as shown below in the second statement the query does not pull data. I felt it could be a an operator issue, but after trying multiple scenarios I cannot get a data pull from the tables when the second condition is added to the WHERE clause. Any help would be greatly appreciated.
Thank you-


SINGLE CONDITION:

SELECT [Anton Time Reporting].CtecId, [Anton Time Reporting].StaffName, [Anton's Reporting Subform].StartDate, [Anton's Reporting Subform].EndDate, [Anton's Reporting Subform].Tasks, [Anton's Reporting Subform].Hours

FROM [Anton Time Reporting], [Anton's Reporting Subform]

WHERE [Anton's Reporting Subform].StartDate=[]

UNION SELECT [Christian Time Reporting].CtecId, [Christian Time Reporting].StaffName, [Christian's Reporting Subform].StartDate, [Christian's Reporting Subform].EndDate, [Christian's Reporting Subform].Tasks, [Christian's Reporting Subform].Hours

FROM [Christian Time Reporting], [Christian's Reporting Subform]

WHERE [Christian's Reporting Subform].StartDate=[]

UNION SELECT [Lynn Time Reporting].CtecId, [Lynn Time Reporting].StaffName, [Lynn's Reporting Subform].StartDate, [Lynn's Reporting Subform].EndDate, [Lynn's Reporting Subform].Tasks, [Lynn's Reporting Subform].Hours

FROM [Lynn Time Reporting], [Lynn's Reporting Subform]

WHERE [Lynn's Reporting Subform].StartDate=[];


DUAL CONDITION:

SELECT [Anton Time Reporting].CtecId, [Anton Time Reporting].StaffName, [Anton's Reporting Subform].StartDate, [Anton's Reporting Subform].EndDate, [Anton's Reporting Subform].Tasks, [Anton's Reporting Subform].Hours

FROM [Anton Time Reporting], [Anton's Reporting Subform]

WHERE ((([Anton's Reporting Subform].StartDate)=[]) AND (([Anton's Reporting Subform].EndDate)=[]))

UNION SELECT [Christian Time Reporting].CtecId, [Christian Time Reporting].StaffName, [Christian's Reporting Subform].StartDate, [Christian's Reporting Subform].EndDate, [Christian's Reporting Subform].Tasks, [Christian's Reporting Subform].Hours

FROM [Christian Time Reporting], [Christian's Reporting Subform]

WHERE ((([Christian's Reporting Subform].StartDate)=[]) AND (([Christian's Reporting Subform].EndDate)=[]))

UNION SELECT [Lynn Time Reporting].CtecId, [Lynn Time Reporting].StaffName, [Lynn's Reporting Subform].StartDate, [Lynn's Reporting Subform].EndDate, [Lynn's Reporting Subform].Tasks, [Lynn's Reporting Subform].Hours

FROM [Lynn Time Reporting], [Lynn's Reporting Subform]

WHERE ((([Lynn's Reporting Subform].StartDate)=[]) AND (([Lynn's Reporting Subform].EndDate)=[]));