DOMAIN ERROR: Base class for Class "Page" has not been resolved

[markus1189]

After downloading miserver and )loading it into the interpreter, I get the following:

      )load /tmp/MiServer-3.1.1652/miserver.dws
/tmp/MiServer-3.1.1652/miserver.dws saved Wed Oct 24 06:44:13 2018
      Start './MS3' ⍝ Run the MiServer v3.0 demonstration site
      1 Start './MS3' ⍝ Run the MiServer v3.0 demonstration site
Could not load development environment due to: DOMAIN ERRORSetDelta[29] ref.SALT_Data←ref.⎕NS''
DOMAIN ERROR: Base class for Class "Page" has not been resolved
SetDelta[29] ref.SALT_Data←ref.⎕NS''

I am totally lost on what that means and how to solve it. Disclaimer: APL newbie here ;)