In the Water Levels tab, the Reading Event drop-down list has duplicate entries:
This is a bug in the gINT Std US Lab.GLB library. To fix this:
Go to Data Design->Library Data.
In the big yellow drop-down list, select WATER LEVEL EVENT.
Delete the three rows with numeric codes. This will leave the three rows with the codes AD, ATD and EOD.
Go to Input->Main Group>Water Levels.
In the Reading Event column, if you see a number instead of a letter code re-select the proper code.