Queries :: Update Query To Remove Values In Field

What I have a a form that my lab supervisor would use. That person selects the records that are to be modified and assigns work, completes work or otherwise updates the status of the records. One of the options is to mark a record as not having a sample here if it has already been marked as having been here. So essentially, I want to modify the record to change the sample arrival date and sample number field (which is a foreign key field) to null or empty. I have created a delete query that deletes the corresponding record just fine.I just am having difficulty updating the two fields mentioned above. When the supervisor selects the record the primary key for that record is also picked up so it is easy to know exactly what record to adjust. The query returns the information to be updated just fine, it just doesn't do that. Here is the sql of the query. As I said, I don't care if the fields are empty or null. Also the fields aren't required.

Code:
UPDATE TestRequestTable SET TestRequestTable.SampleLocation = "", TestRequestTable.SampleArrivalDate = ""
WHERE (((TestRequestTable.TestRequestNumber)=[Forms]![LabScheduleForm]![TRNumberCombo]));