Impossible to enter mail forwarding destination address

IE8 reports the following error message when attempting to either select or type in the destination email address for a mailforward setting:

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; MALC)

Timestamp: Tue, 31 May 2011 10:10:36 UTC

Message: 'document.ModifyUserBean.selectedAttributes.2.checked' is null or not an object

Line: 629

Char: 2

Code: 0

URI: http://admanagerplus:8080/ModifyBulkUser.do?methodToCall=modifyAction&selectedTab=admin&reportId=1009

Message: 'document.ModifyUserBean.selectedAttributes.2.checked' is null or not an object

Line: 629

Char: 2

Code: 0

URI: http://admanagerplus:8080/ModifyBulkUser.do?methodToCall=modifyAction&selectedTab=admin&reportId=1009

Message: 'document.ModifyUserBean.selectedAttributes.2.checked' is null or not an object

Line: 629

Char: 2

Code: 0

URI: http://admanagerplus:8080/ModifyBulkUser.do?methodToCall=modifyAction&selectedTab=admin&reportId=1009

Message: 'document.ModifyUserBean.selectedAttributes.2.checked' is null or not an object

Line: 629

Char: 2

Code: 0

URI: http://admanagerplus:8080/ModifyBulkUser.do?methodToCall=modifyAction&selectedTab=admin&reportId=1009