To enable motion blur in Solaris you need your camera and geometry setup correctly.

For the camera make sure you have the desired shutter window set (you may also need to make sure "Disable Motion Blur" is not enabled on your Render Settings LOP).  The geometry needs the correct attributes and the right settings applied using a Render Geometry Settings LOP node.

The relevant settings can be found under RenderMan > Prototype Attributes > Motion Blur.

First make sure "Enable Motion Blur" is set.
Then choose the relevant settings for your motion blur type in the "Velocity Blur" Setting.

No Velocity Blur

Without velocity motion blur, RenderMan uses all the positions samples provided to it at times between between the shutter window. You must therefore make sure you provide more than one position sample. The Cache LOP node can be used to keep the position samples at the frames before and after or you can use the Motion Blur LOP node to write out sub frame samples.

Velocity Blur

The "velocities" attribute is used to give the direction the positions are moving at that point in time. RenderMan uses these to generate points at the start and end of the shutter window.

Acceleration Blur

The "accelerations" and "velocities" attributes are used in combination to generate points in time. This can give less linear results than velocity blur as the positions can bend in a direction or get faster over a subframe. You can use "Geometry Time Samples" to generate more positions and give a smoother looking result but this may have an effect on memory.

Transform Motion Blur

This is computed separately from the point motion blur and will transform the entire geometry. Like "No Velocity Blur" you need to make sure you have multiple samples of transforms for RenderMan to read. You can change the number of transform time samples using the "Transform Time Samples" setting.