After creating %ZSTART in %SYS, Studio can't log on

I created %ZSTART, having just learned about it. I included some minimal code to test it, as follows:
%ZSTART
SYSTEM
         WRITE "SYSTEM.",!
         QUIT
JOB
         WRITE "JOB.",!
         QUIT
LOGIN
         WRITE "LOGIN.",!
         QUIT
CALLIN
         WRITE "CALLIN.",!
         QUIT

Now Terminal still works as normal, and sure enough I get "LOGIN" displayed, but when I start Studio I get an error message such as the following. I wonder what Caché ODBC has to do with it.

---------------------------
Studio
---------------------------
Unable to log on to server BOBSCACHE, namespace APEX
[Cache ODBC][State : 08S01][Native Code 452]

[C:\PROGRAMS\INTERSYSTEMS\CACHE\BIN\CSTUDIO.EXE]

Message sequencing error
---------------------------
Retry   Cancel   
---------------------------

Any ideas what's happening here please?

Bob