Error message for beam elements

I am running an old version of Algor (Ver. 12)
The model has about 100,000 nodes. When I try to run
the analysis, I get an error message when the beam elemnts are being processed: Cannot match material indicies. The beam elemnts are used to create a gap between solid elemnts and plate elemnts. I put in additional beam elemnts to account for the difference in degrees of freedom.

The model has 13 different groups. There are three different beam groups. The first beam group is #10. When the analysis starts, the first nine groups of plate and brick elements are successfully processed. As soon as group 10 starts, the error mesage appears and the processing stops.

When I run the model check, all groups are processed OK. Just to get the model to run, I changed the beam elements to truss elements. The model ran OK and even processed the remaing two beam element groups. So it will run with truss elemnts (that I don't need) but not the beam elements.

Does any one have any idea why the message appears hwen processing the beam elemnts?

Thanks.