diff --git a/src/opengnsys/httpserver.py b/src/opengnsys/httpserver.py
index 695ab9d..391cc94 100644
--- a/src/opengnsys/httpserver.py
+++ b/src/opengnsys/httpserver.py
@@ -105,6 +105,7 @@ class HTTPServerHandler(BaseHTTPRequestHandler):
                 self.sendJsonError(500, exceptionToMessage(e))
             else:
                 arg0 = e.args[0]
+                while isinstance (arg0, Exception): arg0 = arg0.args[0]      ## handle nested exceptions
                 if type (arg0) is str:
                     logger.debug ('Message processor for "{}" returned exception string "{}"'.format(path[0], str(e)))
                     self.sendJsonError (500, exceptionToMessage(e))