Visual Studio 2010 Web Deployment Project Error

I have a web deployment project in Visual Studio 2010 that is failing to install on a Windows Server 2008 R2 box with error 1603. After turning on msi logging,开发者_JAVA百科 I see:

ERROR  : [06/13/2011 10:54:15:722] [RegisterAspNet]: 
The error indicates that IIS is in 64 bit mode, while this application is a 32 bit application and thus not compatible.

This is indeed a 64 bit box and the app pool I'm trying to install to is indeed 64 bit (Enable 32 bit applications is false, and should be this way)....but all of my dlls are built with Any CPU and the vdproj itself has target platform set to x64...so I don't know why this is failing.

I've also tried enabling IIS 6 Compatibility options for the server, as I've read about others who have had similar problems that have been fixed by doing this...but do so makes no difference.

Anyone encountered this or have any suggestions?

UPDATE: Sort of interesting is that the install fails with two completely conflicting errors:

Running process 'C:\Windows\Microsoft.NET\Framework64\v4.0.30319\aspnet_regiis.exe' with parameters ' -norestart -sn "W3SVC/1/Root/ISV\xxx"' silently...
INFO   : [06/13/2011 12:21:16:329] [RegisterAspNet                          ]: Process Call Result Code: '0'        Process Exit Code: '1'.
ERROR  : [06/13/2011 12:21:16:329] [RegisterAspNet                          ]: The error indicates that IIS is in 32 bit mode, while this application is a 64 bit application and thus not compatible.
INFO   : [06/13/2011 12:21:16:329] [RegisterAspNet                          ]: Trying 32 bit version of 'aspnet_regiis.exe'...
INFO   : [06/13/2011 12:21:16:329] [RegisterAspNet                          ]: Reading registry value Path from key 'HKLM\Software\Microsoft\ASP.NET\4.0.30319.0'...
INFO   : [06/13/2011 12:21:16:329] [RegisterAspNet                          ]: RESULT   Path = 
INFO   : [06/13/2011 12:21:16:329] [RegisterAspNet                          ]: Running process 'C:\Windows\Microsoft.NET\Framework\v4.0.30319\aspnet_regiis.exe' with parameters ' -norestart -sn "W3SVC/1/Root/ISV\xxx"' silently...
INFO   : [06/13/2011 12:21:16:438] [RegisterAspNet                          ]: Process Call Result Code: '0'        Process Exit Code: '1'.
ERROR  : [06/13/2011 12:21:16:438] [RegisterAspNet                          ]: The error indicates that IIS is in 64 bit mode, while this application is a 32 bit application and thus not compatible.
ERROR  : [06/13/2011 12:21:16:438] [RegisterAspNet                          ]: FAILED:  -2147024895
ERROR  : [06/13/2011 12:21:16:438] [RegisterAspNet                          ]: Custom Action failed with code: '0'
INFO   : [06/13/2011 12:21:16:438] [RegisterAspNet                          ]: Custom Action completed with return code: '1'

In the above, it says IIS is in 32 bit mode...then it says it's in 64 bit mode...not sure what's going on here...

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While making changes to Custom Actions in a similar VS2010 Web App Deployment project (which worked perfectly for years), i suddenly started receiving the same exact error sequence on my test server. Google brought me here and to many similar pages, e.g. Application installation error IIS is in 32 bit mode AND IIS is in 64 bit mode. But there are no /, \ or any other non-letter characters in my URL paths!..

Commented all the new code changes, rebuilt, retried .. no joy - same errors. Hm?

Previously built .msi packages showed exactly the same behavior (working fine just a few days ago!), so i figured that the problem must be machine specific.
Well, yes i was also playing with some AppPool settings, fine-tuning the desired mods. But this messing up IIS so badly, that while existing sites work, new ones cannot be installed?! A perspective of being forced to reinstall { ASP.NET | IIS | other web-apps on top of it } did not make me smile..

Then finally i noticed a webapp in the list under Default Web Site - the one i'm making changes to.. Hm?! But all recent installations rolled back after "Custom Action failed: 1603" error, so what is it doing here??

Well, it turns out my very first try failed with exception in new code. It was reported, but MSI did not roll back the installation. Every subsequent attempt was simply stumbling on files and folders that already existed.
So, leftovers from borked install session must be cleaned up manually before retries. Logical.
Once i deleted those, all .msis (old and new) started working again perfectly as before. Shiny! :)

But imagine how easy would it be to fix, if the error message said smth like "File already exists.."?
To quote an answer from linked page: Somebody at Microsoft has to die for this. :)