You need to convert data into actual data type. Let say your input column contains VARCHAR(10) AND output contain VARCHAR(50) then it will fail. If you are using derived column/variable in that case you have to convert data into actual data type. I have samililar issue and then found that at database side it was showing DT_STR(255) BUT DERIVED COLUMN WAS showing DT_wSTR(0) and in derived column no where I specify width but it was comiing default as 0 so then I converted it with

(DT_STR,255,1252)Derived Column variable/function

and then after it worked.

Regards

Daxesh