adding terms in multinom

[ad@cs.uu.nl]

Dear S users,

I'm working with Splus 6 under Windows 2000.

I'm using "multinom" function from the "nnet" library,and
encounter the following problem.

I've created an object called "test.multinom" with a call to the
"multinom" function. Then I call "add1.multinom" with this object
as follows:

> add1.multinom(test.multinom,scope= ~.^2)

and get the error message:

Problem in formula$terms: function "$" not defined for non-vector class
"multinom"

Does anybody have a clue what could be the cause of this error?

Thanks for your help.

-Ad Feelders