Delete Sheet Macro Crashes Excel

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Ok, so I think I found the cause, I have the following formulas in some cells on multiple sheets.

=IF(OR(Incident_Start_Date="",Incident_Start_Date="MM/DD/YY"),"MM/DD/YY",ChangeDateFormat(Incident_Start_Date))

=IF(Incident_Start_Time="HHMM","HHMM",Incident_Start_Time)

=IF(OR((ISERR(ChangeDateFormat(Operational_Period_Begin_Date))),ISERR(ChangeDateFormat(Operational_Period_End_Date))), "MM/DD/YY HHMM - MM/DD/YY HHMM", ChangeDateFormat(Operational_Period_Begin_Date)& " " & Operational_Period_Begin_Time & " - " & ChangeDateFormat( Operational_Period_End_Date) & " " & Operational_Period_End_Time)

Can anyone tell me why these formulas prevents the deletesheet macro form operating correctly?
Is there a way to disable the sheet formulas first then invoke the deletesheet macro?


Gary