Rob,
I compared the searcho2k.asp files both in size, as well as in content. Both were 58 KB, and I used TexpPad to compare the actuall contents to confirm that they were exactly the same, which they were. I didn't think to look at the IIS logs (as obvious as that is!) since the files checked out. So in looking at the IIS Logs now, I do see some differences in the IIS Logs. Here is a copy of the sanitized logs...
/// Logs from Searcho2k.asp that DOES work! ///
#Fields: date time s-ip cs-method cs-uri-stem cs-uri-query s-port cs-username c-ip cs(User-Agent) sc-status sc-substatus sc-win32-status time-taken
2011-02-01 14:38:59 <PRODUCTION_IP_ADDRESS> GET /EnterpriseVault/Searcho2k.asp - 443 - <CLIENT_IP_ADDRESS> Mozilla/4.0+(compatible;+MSIE+7.0;+Windows+NT+5.1;+Trident/4.0;+.NET+CLR+1.1.4322;+.NET+CLR+2.0.50727;+InfoPath.2;+.NET+CLR+3.0.4506.2152;+.NET+CLR+3.5.30729;+MS-RTC+LM+8) 401 2 5 0
2011-02-01 14:38:59 <PRODUCTION_IP_ADDRESS> GET /EnterpriseVault/Searcho2k.asp - 443 <COMAIN\USER_Name> <CLIENT_IP_ADDRESS> Mozilla/4.0+(compatible;+MSIE+7.0;+Windows+NT+5.1;+Trident/4.0;+.NET+CLR+1.1.4322;+.NET+CLR+2.0.50727;+InfoPath.2;+.NET+CLR+3.0.4506.2152;+.NET+CLR+3.5.30729;+MS-RTC+LM+8) 200 0 0 62
2011-02-01 14:38:59 <PRODUCTION_IP_ADDRESS> GET /EnterpriseVault/V9.0.1.1073/en/Dialog.css - 443 - <CLIENT_IP_ADDRESS> Mozilla/4.0+(compatible;+MSIE+7.0;+Windows+NT+5.1;+Trident/4.0;+.NET+CLR+1.1.4322;+.NET+CLR+2.0.50727;+InfoPath.2;+.NET+CLR+3.0.4506.2152;+.NET+CLR+3.5.30729;+MS-RTC+LM+8) 200 0 0 0
2011-02-01 14:38:59 <PRODUCTION_IP_ADDRESS> GET /EnterpriseVault/dialog.js - 443 - <CLIENT_IP_ADDRESS> Mozilla/4.0+(compatible;+MSIE+7.0;+Windows+NT+5.1;+Trident/4.0;+.NET+CLR+1.1.4322;+.NET+CLR+2.0.50727;+InfoPath.2;+.NET+CLR+3.0.4506.2152;+.NET+CLR+3.5.30729;+MS-RTC+LM+8) 200 0 0 0
2011-02-01 14:38:59 <PRODUCTION_IP_ADDRESS> GET /EnterpriseVault/V9.0.1.1073/en/images/AdvancedSearchIcon.gif - 443 - <CLIENT_IP_ADDRESS> Mozilla/4.0+(compatible;+MSIE+7.0;+Windows+NT+5.1;+Trident/4.0;+.NET+CLR+1.1.4322;+.NET+CLR+2.0.50727;+InfoPath.2;+.NET+CLR+3.0.4506.2152;+.NET+CLR+3.5.30729;+MS-RTC+LM+8) 200 0 0 93
2011-02-01 14:38:59 <PRODUCTION_IP_ADDRESS> GET /EnterpriseVault/V9.0.1.1073/en/images/glass.gif - 443 - <CLIENT_IP_ADDRESS> Mozilla/4.0+(compatible;+MSIE+7.0;+Windows+NT+5.1;+Trident/4.0;+.NET+CLR+1.1.4322;+.NET+CLR+2.0.50727;+InfoPath.2;+.NET+CLR+3.0.4506.2152;+.NET+CLR+3.5.30729;+MS-RTC+LM+8) 200 0 0 109
2011-02-01 14:38:59 <PRODUCTION_IP_ADDRESS> GET /EnterpriseVault/V9.0.1.1073/en/images/powered_by.gif - 443 - <CLIENT_IP_ADDRESS> Mozilla/4.0+(compatible;+MSIE+7.0;+Windows+NT+5.1;+Trident/4.0;+.NET+CLR+1.1.4322;+.NET+CLR+2.0.50727;+InfoPath.2;+.NET+CLR+3.0.4506.2152;+.NET+CLR+3.5.30729;+MS-RTC+LM+8) 200 0 0 187
/// Logs from Searcho2k.asp that is MALFORMED ///
#Fields: date time s-ip cs-method cs-uri-stem cs-uri-query s-port cs-username c-ip cs(User-Agent) sc-status sc-substatus sc-win32-status time-taken
2011-02-01 14:31:02 <RECOVERY_IP_ADDRESS> GET /EnterpriseVault/searcho2k.asp - 443 - <CLIENT_IP_ADDRESS> Mozilla/4.0+(compatible;+MSIE+7.0;+Windows+NT+5.1;+Trident/4.0;+.NET+CLR+1.1.4322;+.NET+CLR+2.0.50727;+InfoPath.2;+.NET+CLR+3.0.4506.2152;+.NET+CLR+3.5.30729;+MS-RTC+LM+8) 401 2 5 0
2011-02-01 14:31:02 <RECOVERY_IP_ADDRESS> GET /EnterpriseVault/searcho2k.asp - 443 <COMAIN\USER_Name> <CLIENT_IP_ADDRESS> Mozilla/4.0+(compatible;+MSIE+7.0;+Windows+NT+5.1;+Trident/4.0;+.NET+CLR+1.1.4322;+.NET+CLR+2.0.50727;+InfoPath.2;+.NET+CLR+3.0.4506.2152;+.NET+CLR+3.5.30729;+MS-RTC+LM+8) 200 0 0 218
2011-02-01 14:31:02 <RECOVERY_IP_ADDRESS> GET /EnterpriseVault/V9.0.0.1193/en/Dialog.css - 443 - <CLIENT_IP_ADDRESS> Mozilla/4.0+(compatible;+MSIE+7.0;+Windows+NT+5.1;+Trident/4.0;+.NET+CLR+1.1.4322;+.NET+CLR+2.0.50727;+InfoPath.2;+.NET+CLR+3.0.4506.2152;+.NET+CLR+3.5.30729;+MS-RTC+LM+8) 404 0 2 0
2011-02-01 14:31:03 <RECOVERY_IP_ADDRESS> GET /EnterpriseVault/V9.0.0.1193/en/images/AdvancedSearchIcon.gif - 443 - <CLIENT_IP_ADDRESS> Mozilla/4.0+(compatible;+MSIE+7.0;+Windows+NT+5.1;+Trident/4.0;+.NET+CLR+1.1.4322;+.NET+CLR+2.0.50727;+InfoPath.2;+.NET+CLR+3.0.4506.2152;+.NET+CLR+3.5.30729;+MS-RTC+LM+8) 404 0 2 0
2011-02-01 14:31:03 <RECOVERY_IP_ADDRESS> GET /EnterpriseVault/V9.0.0.1193/en/images/powered_by.gif - 443 - <CLIENT_IP_ADDRESS> Mozilla/4.0+(compatible;+MSIE+7.0;+Windows+NT+5.1;+Trident/4.0;+.NET+CLR+1.1.4322;+.NET+CLR+2.0.50727;+InfoPath.2;+.NET+CLR+3.0.4506.2152;+.NET+CLR+3.5.30729;+MS-RTC+LM+8) 404 0 2 15
So, if I'm not mistaken, it looks like it might be having problems with the "/EnterpriseVault/V9.0.0.1193/en/Dialog.css" file???