AFAIK, JNIPort works with 7.10.1. The method LPSECURITY_ATTRIBUTES is defined in Win32SystemSupport and part of the package OS-ExternalProcess, which is part of Base VisualWorks.
The message seems to indicate that Win32SystemSupport is recompiled while loading DLLCC as a prerequisite of JNIPort. If you manually load DLLCC before loading JNIPort, the problem does not appear.
As far as I can judge, the error message has nothing to do with JNIPort. I don’t know why autoloading DLLCC recompiles an ExternalInterface subclass before loading the compiler for external interfaces.