diff --git a/omci_handlers.go b/omci_handlers.go
index 66007e6..1f0e919 100644
--- a/omci_handlers.go
+++ b/omci_handlers.go
@@ -20,6 +20,7 @@
 	"encoding/binary"
 	"errors"
 	"log"
+	"fmt"
 )
 
 type OmciMsgHandler func(class OmciClass, content OmciContent, key OnuKey) ([]byte, error)
@@ -199,8 +200,8 @@
 		pkt[11] = state.uniGInstance // UNI-G ME Instance
 		state.uniGInstance++
 	default:
-		log.Printf("Invalid MibUpload request %d", state.mibUploadCtr)
-		//return nil, errors.New("Invalid MibUpload request")
+		errstr := fmt.Sprintf("Invalid MibUpload request: %d", state.mibUploadCtr)
+		return nil, errors.New(errstr)
 	}
 
 	state.mibUploadCtr++
diff --git a/omci_sim.go b/omci_sim.go
index a428cb7..20fe8be 100644
--- a/omci_sim.go
+++ b/omci_sim.go
@@ -41,8 +41,10 @@
 
 	resp, err = Handlers[msgType](class, content, key)
 	if err != nil {
-		return resp, err
+		log.Println("%s", err)
+		return resp, nil
 	}
+
 	resp[0] = byte(transactionId >> 8)
 	resp[1] = byte(transactionId & 0xFF)
 	resp[2] = 0x2<<4 | byte(msgType)