Hi,
if your loading the data form ECC to BW is yes,
after replicating the data source check the data source fileds tab- check the object length and type.
ex- ECC field- MATNR - BW info object 0MATERIAL
no need to create the info object use the standard busines object - it is better option.
if business content object not avaliable create the custome info objects.
as raman said use the table RSOSFIELDMAP for standard objects.
-Phani.