Lookup does not work

All

I am trying to get a date by certain criterias (serial no. and Product type) since I need to calculate the difference between those dates in month in order to calculate the correct quantity of periods to release the revenue. I created the following measure:

MEASURE =

VAR Category = TABLE[Revenue Model Category]

VAR boolean_LicTypeOther = TABLE[License type]= "Other"

VAR boolean_LicTypePrptl = TABLE[License type] = "Perpetual"

VAR boolean_LicTypeFlex = TABLE[License type] = "Flex"

VAR boolean_Schuetz_Prptl_Core = TABLE[License type] = "Perpetual" && TABLE[Life cycle] = "New" && TABLE[Product type] = "Core Version"

VAR boolean_Module = TABLE[Product type] = "Module" && TABLE[License type] = "Perpetual"

VAR FOT_Adjusted = TABLE[FOT_Adjusted]

VAR UpgradeContract = TABLE[License type] = "Perpetual" && TABLE[Life cycle] = "Extended"

VAR boolean_serialno_Core = CALCULATETABLE(TABLE, ALL(TABLE[serialNumber], TABLE[Product type], TABLE[FOT_Convention]),TABLE[serialNumber] <> Blank (),TABLE[Product type] = "Core Version")

VAR boolean_serialno_Module = CALCULATETABLE(TABLE, ALL(TABLE[serialNumber], TABLE[Product type], TABLE[FOT_Convention]),TABLE[serialNumber] <> Blank (),TABLE[Product type] = "Module")

VAR boolean_serialno = CALCULATETABLE(TABLE, FILTER(TABLE, TABLE[serialNumber] <> Blank ()))

VAR boolean_fot_cv = LOOKUPVALUE(TABLE[Date], TABLE[serialNumber],  DISTINCTCOUNTNOBLANK([serialNumber]) , TABLE[Product type], "Core Version")

VAR boolean_fot_module = LOOKUPVALUE(TABLE[Date], TABLE[serialNumber], DISTINCTCOUNTNOBLANK([serialNumber]), TABLE[Product type], "Module")

VAR boolean_Module_New = TABLE[Product type] = "Module" && TABLE[Life cycle] = "New"

RETURN

    SWITCH (

            True,

            Category IN {"xx", "yy", "zz" },

                SWITCH (

                    TRUE,

                    boolean_LicTypeOther, 1,

                    boolean_LicTypePrptl, 12,

                    boolean_LicTypeFlex, 12,

                    boolean_Module_New && NOT ISBLANK (FOT_Adjusted), 12 - DATEDIFF(boolean_fot_module, boolean_fot_cv,  MONTH),

                        12),

            Category IN { "aa"},

                SWITCH (

                    TRUE,

                        boolean_Schuetz_Prptl_Core, 37,

                        boolean_Module && ISBLANK (Fot_Adjusted), 18,

                        boolean_LicTypeOther, 1,

                        boolean_Module && NOT ISBLANK (FOT_Adjusted) && TABLE[Life cycle] = "New", 37,

                        12),

            Category IN { "bb" },

                SWITCH (

                    TRUE,

                       UpgradeContract, 1,

                        48),

            Category IN { "cc" },

                SWITCH (

                    TRUE,

                        UpgradeContract || boolean_LicTypeOther, 1,

                        boolean_LicTypeFlex,  12,

                        1),

            Category IN { "dd" },

                SWITCH (

                    TRUE,

                        boolean_LicTypeOther || boolean_LicTypePrptl, 1,

                        12),

            BLANK ()

            )

I am not sure if I am on the right track, but I am getting nowhere. Now I get the typical message Function "'LOOKUPVALUE' does not support comparing values of type Text with values of type Integer. Consider using the VALUE or FORMAT function to convert one of the values." Since SerialNumber and Product type are both text, I assume the culprit is the date, but I do not know how to convert this actually. Does someone has an idea? And i searched this forum and the internet in general to no avail. 

Currently:

Should be:

I also think that I have to consider the fact that the Core Version might be older than 1 year so I need the latest FOT_Convention date for this - if that makes sense. the result for the measure should be between 0 and 12.

Pls  let me know if you needf any additional information!

Thanks everyone!