You can try the following steps.
1. Reboot the mac, if that doesn't help.
2. Read the article I wrote down here: http://planetvm.net/blog/?p=3240
If that still doesn't help, you might be running out of character device major numbers. You can read about that here: Fusion 5 - Could not open /dev/vmmon: No such file or directory.
Wil| Author of Vimalin. The virtual machine Backup app for VMware Desktop Products
| Vimalin : Automated backups for VMware Fusion and VMware Workstation Professional
| More info at https://www.vimalin.com
| Twitter @wilva
| VMware Wiki at http://www.vi-toolkit.com
Thank you so much!!! It worked the first time and saved me a lot of headaches.