Failed to load Sage session: VB + Sage 3.15

edit

I have Sage 5.13 and VirtualBox 4.3.2 downloaded and installed on a Win7 machine. First time I run the programs everything works well, when I try to reopen the files I left in VB (Save machine state), I get the following error message:

Failed to open a session for the virtual machine Sage-5.13.

Failed to load unit 'PATM' (VERR_SSM_LOADED_TOO_MUCH).

Result Code: E_FAIL (0x80004005) Component: Console Interface: IConsole {8ab7c520-2442-4b66-8d74-4ff1e195d2b6}

I tried to download the majority of the notebooks I worked on and leave in VB only one, however, the message appears again.