When I try to access HTMLArea in the Admin area of my site I get the following error being generated by IE8

Webpage error details

User Agent: Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 6.1; Trident/4.0; SLCC2; .NET CLR 2.0.50727; .NET CLR 3.5.30729; .NET CLR 3.0.30729; Media Center PC 6.0; OfficeLiveConnector.1.4; OfficeLivePatch.1.3)
Timestamp: Wed, 16 Dec 2009 21:25:08 UTC


Message: 'HTMLArea' is undefined
Line: 30
Char: 7
Code: 0
URI: http://:censored:/:censored:/:censor...age&vcheck=yes


Message: 'HTMLArea' is undefined
Line: 20
Char: 39
Code: 0
URI: http://:censored:/:censored:/:censor...age&vcheck=yes

Why won't my HTML editor appear when trying to edit pages? What in God's name does the above error mean? How do I rectify it?

Any help would be appreciated.

Thanks

JB Webb-Benjamin