Calculation error SUMX in table

Hello all,

I want to create a measure to calculate the Current Ticket  based on the following code:

Current Ticket = var currentDate = MAX(OWK_CI_INCIDENTS[IDT_STARTDATUM].[Date]) return SUMX(FILTER(ALL(OWK_CI_INCIDENTS);MONTH(OWK_CI_INCIDENTS[IDT_STARTDATUM].[Date])=MONTH(currentDate)&&YEAR(OWK_CI_INCIDENTS[IDT_STARTDATUM].[Date])=YEAR(currentDate));[REMEDYTICKET_NUMBER])

Unfortunat;y i have the following error message :

The data type for OWK_CI_INCIDENTS[IDT_STARTDATUM].[Date])  is Date   and for REMEDYTICKET_NUMBER is Text.

Thanks for your help!