I've seen this issue before. I'm assuming the configuration file gets corrupted, possibly during a computer crash. I've moved away from configuration files with the version I'm currently working on.
You need to delete the "user.config" file from the following location for the current version of Sony Vegas. Only a few settings are stored in it so you won't lose anything important. Settings include recently used celebrations from the burn tab, and some language specific
settings like the name of the black video and the keys sent to DVD Architect. If you haven't changed them, it will pick up the default one's for you.
"C:\Users\Mick\AppData\Local\Sony_Creative_Software_In"
On my computer, the exact location is below but yours may differ depending on operating system, language and the version of Sony Vegas.
"C:\Users\Mick\AppData\Local\Sony_Creative_Software_In\Script_Domain_Path_vc ucme4f4bggofbga1ba1ktqycv4k3ls\Version_13.0_(Build_373)_64-bit"
You will need to turn on hidden files to see this location.
Apologies for the issue. I have a task logged to check for the error and offer to delete the configuration file but you'll have to do it manually for the moment. I have no idea what causes it but it's a Microsoft .Net problem.
Cheers. Mick.