Error when trying to add/modify list columns

SP 2010 Foundation, single server.

I have a custom list I'm trying to add a colum to. I add the column, provide "Name and Type", and click OK. Nothing happens except for an IE error:

Webpage error details

User Agent: Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 6.1; WOW64; Trident/4.0; SLCC2; .NET CLR 2.0.50727; .NET CLR 3.5.30729; .NET CLR 3.0.30729; Media Center PC 6.0; .NET4.0C; MS-RTC EA 2; .NET4.0E)
Timestamp: Fri, 19 Oct 2012 16:41:33 UTC

Message: 'undefined' is null or not an object
Line: 1426
Char: 4
Code: 0
URI: http://www.sitename.com/_layouts/FldEdit.aspx?List=%7BB6383018%2D2F26%2D4F03%2D9150%2D2328617675BC%7D&Field=Body

 Look familiar? Recommendations?

Thanks,

Scott