Oracle SQL comments fail with [99999][17439] Invalid SQL type: sqlKind = UNINITIALIZED

I am unable to execute a SQL script with comments in it.  Either comments that begin with -- or comments like /* ... */.  If I execute the comment by itself I get the error [99999][17439] Invalid SQL type: sqlKind = UNINITIALIZED:

sql> /*** Roles ***/
[2017-11-14 19:02:11] [99999][17439] Invalid SQL type: sqlKind = UNINITIALIZED

If I execute the script with the comments in it, it fails with:

sql> /*** Roles ***/
DELETE FROM EPP_DEV."UserRoles";
[2017-11-14 19:01:15] [42000][933] ORA-00933: SQL command not properly ended

Any idea how I can fix this?

I am using the Oracle thin client, the oracle.jdbc.OracleDriver and the Oracle SQL*Plus dialect.

Thanks for your help!