The SAS/IML documentation on calling R says:
"The result of an R analysis can be a complicated structure. In order to transfer an R object via the previously mentioned methods and modules, the object must be coercible to a data frame. (The R object m can be coerced to a data frame provided that the function as.data.frame(m) succeeds.) There are many data structures that cannot be coerced into data frames. As the example in the next section shows, you can use R statements to extract and transfer simpler objects."
The doc then shows an example.