For the dynamic calculation of a single-span beam, I get the message:
"Too many eigenvalue required, maximum number = 0 ...".
However, I just specified one eigenvalue for determination!
The natural vibrations of the single-span beam cannot be determined if the masses act only in the Z-direction and the internal member partition is defined as "1." The displacement component of the member in Z-direction can be determined only with an internal member division greater than 1.
Alternatively, you can divide the member in RSTAB by nodes and thus create several partial members. In this way, you can determine the natural frequency also for a member division of "1" at the intermediate nodes.