reportbuilder.application Authentication Error

This is the strangest thing. Whenever I try to access report builder from 90% of machines, I get the following error:

PLATFORM VERSION INFO
Windows : 5.1.2600.131072 (Win32NT)
Common Language Runtime : 2.0.50727.42
System.Deployment.dll : 2.0.50727.42 (RTM.050727-4200)
mscorwks.dll : 2.0.50727.42 (RTM.050727-4200)
dfdll.dll : 2.0.50727.42 (RTM.050727-4200)
dfshim.dll : 2.0.50727.42 (RTM.050727-4200)

SOURCES
Deployment url : https://reports.mysite.com/ReportServer/ReportBuilder/ReportBuilder.application

ERROR SUMMARY
Below is a summary of the errors, details of these errors are listed later in the log.
* Activation of https://reports.mysite.com/ReportServer/ReportBuilder/ReportBuilder.application resulted in exception. Following failure messages were detected:
+ Downloading https://reports.mysite.com/ReportServer/ReportBuilder/ReportBuilder.application did not succeed.
+ The remote server returned an error: (401) Unauthorized.

COMPONENT STORE TRANSACTION FAILURE SUMMARY
No transaction error was detected.

WARNINGS
There were no warnings during this operation.

OPERATION PROGRESS STATUS
* [5/10/2006 8:48:02 AM] : Activation of https://reports.mysite.com/ReportServer/ReportBuilder/ReportBuilder.application has started.

ERROR DETAILS
Following errors were detected during this operation.
* [5/10/2006 8:48:11 AM] System.Deployment.Application.DeploymentDownloadException (Unknown subtype)
- Downloading https://reports.mysite.com/ReportServer/ReportBuilder/ReportBuilder.application did not succeed.
- Source: System.Deployment
- Stack trace:
at System.Deployment.Application.SystemNetDownloader.DownloadSingleFile(DownloadQueueItem next)
at System.Deployment.Application.SystemNetDownloader.DownloadAllFiles()
at System.Deployment.Application.FileDownloader.Download(SubscriptionState subState)
at System.Deployment.Application.DownloadManager.DownloadManifestAsRawFile(Uri& sourceUri, String targetPath, IDownloadNotification notification, DownloadOptions options, ServerInformation& serverInformation)
at System.Deployment.Application.DownloadManager.DownloadDeploymentManifestDirectBypass(SubscriptionStore subStore, Uri& sourceUri, TempFile& tempFile, SubscriptionState& subState, IDownloadNotification notification, DownloadOptions options, ServerInformation& serverInformation)
at System.Deployment.Application.DownloadManager.DownloadDeploymentManifestBypass(SubscriptionStore subStore, Uri& sourceUri, TempFile& tempFile, SubscriptionState& subState, IDownloadNotification notification, DownloadOptions options)
at System.Deployment.Application.ApplicationActivator.PerformDeploymentActivation(Uri activationUri, Boolean isShortcut)
at System.Deployment.Application.ApplicationActivator.ActivateDeploymentWorker(Object state)
Inner Exception
System.Net.WebException
- The remote server returned an error: (401) Unauthorized.
- Source: System
- Stack trace:
at System.Net.HttpWebRequest.GetResponse()
at System.Deployment.Application.SystemNetDownloader.DownloadSingleFile(DownloadQueueItem next)

COMPONENT STORE TRANSACTION DETAILS
No transaction informtion is available.
-

Ok, so here's the catch. It works one 1 machine, a co-workers machine. I can login as any user and it'll work fine. But when I try it on any other machine, including my laptop, my desktop, my server, etc. I get that error. I've tried adjusting the IE Security settings, firewall settings, even tried different browsers. Here's some of the stuff installed on my machines:

Laptop
-Windows XP Pro
-ASP.NET Validation Tool
-Visual Basic Express w/ SQL Server Express
-.NET 1.1/2.0 Framework

Desktop
-Windows XP Home
-Visual Studio 2005 Professional
-.NET 1.1/2.0 Framework

Server
-Windows Server 2003 Enterprise
-SQL Server 2005
-.NET 1.1/2.0 Framework

Any help on this would be greatly appreciated. Even our lead developer has no clue, it won't work on his machine either!

I found a solution here.