Multivalue paramater not working when single value selected

Hi,

I am using Teradata as Database. I have a multivalue parameter. In my Query i have mapped this paramtere as:

K.REGION IN (@P_Region)

The issue is when i select multiple values it works fine, but i when i select single value it return error that "There is a mistmatch between the number of parameters specified and number of parameteres required".

Any Quick Solution please

regards