ACPI errors

Hi,
I've started getting this error randomly since about 15 days ago.
I've cvsupped yesterday but the error still comes up sometimes.
The system is a Dell Inspiron 5100.


Sleeping on "acsem" with the following non-sleepable
locks held:
exclusive sleep mutex acpica subsystem lock r = 0 (0xc235c9c0) locked _at_
/usr/src/sys/modules/acpi/acpi/../../../dev/acpica/Osd/O
sdSynch.c:360
KDB: stack backtrace:
kdb_backtrace(c09dbe14,e32beb84,1,1,1) at kdb_backtrace+0x2f
witness_warn(5,c235cb40,c08cb115,c0baf5ca,c065b845) at
witness_warn+0x1bb
msleep(c235cb40,c235cb40,100,c0baf5ca,0) at msleep+0x58
AcpiOsWaitSemaphore(c235cb40,1,ffff,8,15) at AcpiOsWaitSemaphore+0x1fb
AcpiUtAcquireMutex(7,1,0,0,0) at AcpiUtAcquireMutex+0x8f
AcpiDisableGpe(0,1c,1,c227a7d1,c239f180) at AcpiDisableGpe+0x23
EcGpeHandler(c239f180,1,0,8,102f) at EcGpeHandler+0x3f
AcpiEvGpeDispatch(c2380f50,1c,c227a7dd,27fa10,4) at
AcpiEvGpeDispatch+0xc4
AcpiEvGpeDetect(c230bc20,0,c230bc20,e32bed14,c064f39e) at
AcpiEvGpeDetect+0x12f
AcpiEvSciXruptHandler(c230bc20,0,c08c8452,256,c0990c60) at
AcpiEvSciXruptHandler+0x2a
ithread_loop(c2279880,e32bed48,c08c8251,30e,c2279880) at
ithread_loop+0x157
fork_exit(c064f247,c2279880,e32bed48) at fork_exit+0xc7
fork_trampoline() at fork_trampoline+0x8
--- trap 0x1, eip = 0, esp = 0xe32bed7c, ebp = 0 ---

I'm running with a modified DSDT (downloaded from acpi.sf.net) which I used on 
linux and FreeBSD since the beginning.
Is this normal/not dangerous?

Thanks in advance

Regards
Filippo