Comment 18 for bug 307645

I am having the same problem and have posted on the Mint forum. Here is a copy of that post:

I was running Virtualbox, galculator, opera, firefox thunderbird, keepass, guake, dropbox. When I tried to switch windows from the one virtualbox was running in to opera, the computer became unresponsive. Nothing worked. I had to hold the power button down to shut the system down. I have never had this problem before with any version of Mint. Any ideas?
Here is my system:
System: Host mikew-desktop Kernel 2.6.31-14-generic i686 (32 bit) Distro Linux Mint 8 Helena - Main Edition
CPU: Dual core AMD Athlon 64 X2 6000+ (SMP) cache 2048 KB flags (sse3 nx lm svm) bmips 12055.3
Clock Speeds: (1) 3000.00 MHz (2) 3000.00 MHz
Graphics: Card nVidia C61 [GeForce 6150SE nForce 430] X.Org 1.6.4 Res: 1280x1024@50.0hz
GLX Renderer GeForce 6150SE nForce 430/PCI/SSE2/3DNOW! GLX Version 2.1.2 NVIDIA 185.18.36 Direct Rendering Yes
Audio: Card nVidia MCP61 High Definition Audio driver HDA Intel
Sound: Advanced Linux Sound Architecture Version 1.0.20
Network: Card nVidia MCP61 Ethernet driver forcedeth at port ec00
Disks: HDD Total Size: 500.1GB (43.2% used) 1: /dev/sda ST3500630AS 500.1GB
Partition: ID:/ size: 20G used: 5.1G (28%) fs: ext4 ID:/tmp size: 20G used: 200M (2%) fs: ext3
ID:swap-1 size: 4.09GB used: 0.00GB (0%) fs: swap
Info: Processes 159 Uptime 14 min Memory 291.5/2896.9MB Client Shell inxi 1.2.6