Can we use any item category for Cross selling for inputting item in sales order?

Dear all,

we have tried to use Cross selling function in creation sales order in VA01.

so we finished all IMG setting needs but some material doesn't work Croess selling funtion.

for example) following item(parts) works Cross Selling function.

                     but other item(machine) doesn't work.

is there any difference? we should check sales item category or material item categor?

thanks in advance,

Daniel.