Reporting constant errors:variant data-type cannot be used to define calculated columns

[LIAMLI]

Hi,
I have a table named: FACT_Stock, I want to create a calculated column to define remaining shelf life (months).
Mine methodology is to use Column [EXP], [PictureDate], these two colum type is date, [EXP] is mixed with some blanks.
Formula of Remaining shelf life (months) is written as 

[RSL] =

VAR Months = IF(FACT_Stock[EXP] = BLANK(), BLANK(), DATEDIFF(FACT_Stock[PictureDate],FACT_Stock[EXP],MONTH))

RETURN

IF(

    Months = BLANK(),

    "Undefined",

    SWITCH(

        TRUE(),

        Months <= 0,

        "Expired",

        Months >= 48,

        "Not relevant",

        Months

    )

)

It keeps reporting errors: Expressions that yield variant data-type cannot be used to define calculated columns. I tried serveral ways to fix the error, such as use CONVERT formula to transform data type, but the error doesn't diappear

[PhilipTreacy]

Hi @LIAMLI 

Plese supply a representataive sample of your data (or all of it), so we can see what your working with.  Really hard to debug something without seeing the data.

Regards

Phil

[LIAMLI]

Hi Philip,
Table is like this way

ItemCode	EXP	SOH	PictureDate
H084490001	2021/11/14	70	2024/3/31
H084560001	2022/5/14	60	2024/3/31
H084560001	2022/3/14	13	2024/3/31
H084560001	2022/5/14	40	2024/3/31
H084560001	2999/12/31	10	2024/3/31
H084580001	2022/4/14	60	2024/3/31
H084580001	2022/6/14	14	2024/3/31
H084580001	2022/6/14	6	2024/3/31
H084580001	2023/4/18	50	2024/3/31
H084580001	2022/6/14	15	2024/3/31
CBLM250		19	2024/3/31
CBLM250		36	2024/3/31
CBLM250T		1	2024/3/31
CBLM250T		7	2024/3/31
50551	2026/12/20	439	2024/3/31
49831	2026/7/18	3829	2024/3/31
49831	2026/7/18	5	2024/3/31
50551	2026/6/21	15722	2024/3/31
49831	2026/3/31	1	2024/3/31
50941	2026/3/30	496	2024/3/31
CL20811T		34	2024/3/31
CL20811T		767	2024/3/31
CL20811TT		9	2024/3/31
H282030001	2099/1/1	12	2024/4/1
H282050001	2099/1/1	54	2024/4/1
H285010001	2099/1/1	15	2024/4/1
H328010001	2099/1/1	9875	2024/4/1