Guest almost freezes (100% CPU load) when trying to access disk - nothing written to file.

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This freezes I am observing with every single version of VBox > 4.0.4.

I usually have a VM with OS/2 4.5 up and running fine daily. This VM almost never gets shut down, it is just saved and also survives 100's of Suspends of the host (s2ram). Starting with VBox 4.0.6 the VM worked fine onlyy for some 10 save/s2ram cycles, then suddenly CPU load in the VM gous up to 100% and the "green dot" at the bottom of the VBox-window indicates continous disk (read)-access to the virtual disk, however host indicates zero disk/file activity.

I finally set up a separate test system with Squeeze-amd64 and VBox 4.1.0 and a known good VDI attached as immutable. Yesterday the above described situation happened: first mouse clicks get delayed and finally lost, CPU-load up at 100%, disk activity 100% in VBox window (bottom). I saved this situation and do attach several log files:

a) VBox-frozen.log (Guest-log where VM started working, then froze at the end, saved VM)
b) VBox-starting-frozen-VM.log (opening the saved + frozen VM today, still the same, saved again)
c) VirtualBox-home.tgz (all global configuration files including logs)

Important thes global log files contain lot of ERROR entries like:

00:00:04.438 nspr-2   ERROR [COM]: aRC=VBOX_E_INVALID_VM_STATE (0x80bb0002) aIID={5eaa9319-62fc-4b0a-843c-0cb1940f8a91} aComponent={Machine} aText={Machine is not locked for session (session state: Unlocked)}, preserve=false
00:08:27.310 nspr-2   ERROR [COM]: aRC=VBOX_E_IPRT_ERROR (0x80bb0005) aIID={5eaa9319-62fc-4b0a-843c-0cb1940f8a91} aComponent={Machine} aText={Saved screenshot thumbnail data is not available (VERR_NOT_SUPPORTED)}, preserve=false
00:08:37.453 main     ERROR [COM]: aRC=VBOX_E_OBJECT_IN_USE (0x80bb000c) aIID={53f9cc0c-e0fd-40a5-a404
....

As mentioned above the VM has an immutable VDI file and one snapshot.

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guest log with VM almost frozen at the end. VM saved.

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guest log starting a saved and frozen VM, closing by "save" again

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global VBox configuration files incl. logs wit lot of ERROS's