vixdisklib_Open fail in vsphere 4.1 with many disks

when I use vixdisklib_open the esx4.1 disks, the first disk is works well,but then open the second disk, vixdisklib_open return a error value 1(unknow error). only in vsphere 4.1 has this issue. anyone know why?

the fial scene

1、I use vmware vshpere client create a VM

2、then I create a other virtual disk for the VM.

3、I use vddk API (vixdisklib_open)to open VM disks,  the first disk goes well, but the second disk return a error value 1.

the success scene

1、I use vmware vshpere client create a VM

2、then I create a other virtual disk for the VM.

3、I take a snapshot for the VM, then I use vddk API (vixdisk_open)to open vm disks, the tow disk all go well with no error.

anyone has see this issue.

thanks