Index: /trunk/src/VBox/Devices/Storage/DevAHCI.cpp
===================================================================
--- /trunk/src/VBox/Devices/Storage/DevAHCI.cpp	(revision 36991)
+++ /trunk/src/VBox/Devices/Storage/DevAHCI.cpp	(revision 36992)
@@ -1127,4 +1127,8 @@
     }
 
+    if (   (u32Value & AHCI_PORT_SERR_N)
+        && (pAhciPort->regSERR & AHCI_PORT_SERR_N))
+        ASMAtomicAndU32(&pAhciPort->regIS, ~AHCI_PORT_IS_PRCS);
+
     pAhciPort->regSERR &= ~u32Value;
 
@@ -1374,5 +1378,6 @@
 
         /* Send the first D2H FIS only if it wasn't already send. */
-        if (!pAhciPort->fFirstD2HFisSend)
+        if (   !pAhciPort->fFirstD2HFisSend
+            && pAhciPort->pDrvBase)
         {
 #ifndef IN_RING3