diff --git a/exchangelib/util.py b/exchangelib/util.py
index ce5f96d..019b97f 100644
--- a/exchangelib/util.py
+++ b/exchangelib/util.py
@@ -186,6 +186,7 @@ def set_xml_value(elem, value, version):
     from .ewsdatetime import EWSDateTime, EWSDate
     from .fields import FieldPath, FieldOrder
     from .folders import EWSElement
+    from .version import Version
     if isinstance(value, string_types + (bool, bytes, int, Decimal, datetime.time, EWSDate, EWSDateTime)):
         elem.text = value_to_xml_text(value)
     elif isinstance(value, RestrictedElement):
@@ -195,6 +196,8 @@ def set_xml_value(elem, value, version):
             if isinstance(v, (FieldPath, FieldOrder)):
                 elem.append(v.to_xml())
             elif isinstance(v, EWSElement):
+                if not isinstance(version, Version):
+                    raise ValueError("'version' %r must be a Version instance" % version)
                 elem.append(v.to_xml(version=version))
             elif isinstance(v, RestrictedElement):
                 elem.append(v)
@@ -205,6 +208,8 @@ def set_xml_value(elem, value, version):
     elif isinstance(value, (FieldPath, FieldOrder)):
         elem.append(value.to_xml())
     elif isinstance(value, EWSElement):
+        if not isinstance(version, Version):
+            raise ValueError("'version' %s must be a Version instance" % version)
         elem.append(value.to_xml(version=version))
     else:
         raise ValueError('Unsupported type %s for value %s on elem %s' % (type(value), value, elem))
diff --git a/exchangelib/version.py b/exchangelib/version.py
index 03d3f0f..56424a1 100644
--- a/exchangelib/version.py
+++ b/exchangelib/version.py
@@ -201,13 +201,12 @@ def guess(cls, protocol):
     @classmethod
     def _guess_version_from_service(cls, protocol, hint=None):
         # The protocol doesn't have a version yet, so add one with our hint, or default to latest supported version.
-        # Use ConvertId as a minimal request to the server to test if the version is correct. If not, ConvertId will
-        # try to guess the version automatically. Make sure the call to ConvertId does not require a version build.
-        from .properties import ENTRY_ID, EWS_ID, AlternateId
-        from .services import ConvertId
+        # Use ResolveNames as a minimal request to the server to test if the version is correct. If not, ResolveNames
+        # will try to guess the version automatically.
+        from .services import ResolveNames
         protocol.version = Version(build=None, api_version=hint or API_VERSIONS[-1])
         try:
-            list(ConvertId(protocol=protocol).call([AlternateId(id="DUMMY", format=EWS_ID, mailbox="DUMMY")], ENTRY_ID))
+            list(ResolveNames(protocol=protocol).call(unresolved_entries=[protocol.credentials.username]))
         except (ErrorInvalidSchemaVersionForMailboxVersion, ErrorInvalidServerVersion):
             raise TransportError('Unable to guess version')
         except ResponseMessageError: