[7/13/07: See this post for the solution!]

I have run into a bizarre problem with ClickOnce that is occuring with IE7 on both of my Vista computers.

Both computers have Visual Studio 2005 SP1 and the special vista version of VS2005 SP1. And on both of these, I can’t use clickonce to install apps from  Internet Explorer. The ClickOnce mechanism wants me to install .NET.

Firefox doesn’t have this problem. (Check out this earlier post.)

Here is a SIMPLE little nothing Hello World app. The only thing in it is this form which has ZERO .NET 3.0 stuff in it. It is pure .NET 2.0.

When I set the publish properties with NO prerequisites at all:

it still wants me to install .NET (on a Vista machine with .NET 2 and .Net 3 already there by default!)

I get the same effect if I run the publisher saying “yes, build a setup exe” with NO prerequisites installed.

If I give in and Install anyway, it gets stranger. It is installing WinFX Beta 2! I have actually let it go all the way through prior to this, which is why in this case it is saying “repair,etc…”.

Even if I follow through the installation, ClickOnce continues to insist that I install it (again and again) so I can never launch /install my application.

This partciular computer has a new hard drive that I bought a few months ago on which I installed Vista Ultimate RTM, VS2005 and the service packs. No beta software has ever touched this metal.

I have done the same tests on my 2 month old laptop which also has Vista. I get the exact same results.

I have been at DevTeach for most of this week. A number of very (very) smart people who were at the conference looked at this and were equally mystified.

Brian Noyes created a hello world app in front of me and ran it with no problems.

John Bristowe pointed out the fact that it says “The following preqrequisites are required:” with nothing listed below. WIth no pre-reqs, that statement shouldn’t exist. He checked the manifest and researched the schema of the manifest and still remained mystified.

Derek Hatchard spent some time looking at the page headers to see why IE and FF behaved differently.

Prior to DevTeach, I spent many hours trying to figure this out because it was having a pretty bad effect on the demos for one of my talks at DevTeach. At DevTeach, I spent every free minute trying to solve this problem (oh and another annoyance that has to do with IIS7 being super-secure…).

I left a post in the ClickOnce forum on Monday and it has qquickly gotten buried under two pages of questions that have been asked since then, and gone unanswered. It’s a little scary how many questions people are asking on that forum.

So, I am putting it here in case anyone recognizes this problem and knows what to do about it. It sure made doing my ClickOnce session at DevTeach challenging, to say the least!

Update: at this point, I can tell the problem is not about IIS7, but it must be my computers. Once the problem began on these boxes, it now happens when, from either of these computers, I try to hit a ClickONce deployment site that is on an IIS6 server.