SharePoint 404 error after Update-SPSolution - sharepoint-2010

Question

I got an 404 error after I update a SharePoint 2010 solution, and I dont know the reason why.
I have analysed the log file, the update process was successfull, all changed files have been replaced, added or deleted. Log is telling that the update was successfull too. After opening the SiteCollection via Browser, a 404 error is shown, the sitecollection is not reachable.
What have I changed in the solution:
Added two Element files
Removed a unused empty Feature
Removed an obsolete custom MasterPage
Added a custom UserControl
The WebConfig is updated successfull, and it includes the assembly in the SafeControls, with the right values.
The Content Database for this deployed solution seems to be fine too.
The SiteCollection settings are reachable via PowerShell. The collection does exists in the configuration and all values seems to be fine too.
I checked with Fiddler too. It says that there is no file. I have done a IIS reset for sure too, multiple times.
I have no problems to create a new site collection with the updated solution. And the last things to add: There were no changes to ListDefinitions, ContentTypes. Only some changes to the ONET.xml have been done (removing the custom masterpage from the site definition).
Hopefully someone has ever got this issue and knows how to deal with it.

Answer 1

I got the solution and I would like to share with you. I think its a bug in SharePoint 2010 which is not well documented.. or even not documented.
Following scenario: We have already a deployed package with a custom masterpage. We are now in the situation where we need to rename or remove the masterpage from the package. We were performing a Update-SPSolution and the result is a 404 error for that specific sitecollection. When we analyse the logs or any other part we will get no errors, no information's for this bug, everything from the log seems to work fine.
But that’s a lie. In that moment where we have performed the update the masterpage assigned to that specific site collection is gone and occurs a null exception during initialization, which gets not logged. The 404-Error is the result.
I spend now a day for developing a fix. Before we proceed with the update we have to remove and to reference the solution with a different masterpage. This can be done by PowerShell. For example it could look like this:
# Delte old custom masterpage
$web = get-spweb http://development/mysite
$lib =$web.GetFolder("_catalogs/masterpage")
$file = $lib.Files["MyMaster.master"];
$file.Delete();
$web.Dispose();
# Revert Branding to SP Default
$site = Get-SPSite http://development/mysite
$site | Get-SPWeb -limit all | ForEach-Object { $_.MasterUrl = $_.ServerRelativeUrl + "/_catalogs/masterpage/v4.master";$_.Update() }
$site.Dispose()
After we have removed the masterpage manually we can proceed with the solution update and everything will work fine. Hope this will help anyone who is in the same situation.
Update:
I recognize that sometimes powershell is not ably to delete the masterpage. This is because the masterpage is still in memory. Therefore we need to clean the GC. Therefore here the updated script:
Delte old custom masterpage
[System.GC]::Collect()
[System.GC]::WaitForPendingFinalizers()
$web = get-spweb http://development/mysite
$lib =$web.GetFolder("_catalogs/masterpage")
$file = $lib.Files["MyMaster.master"];
$file.Delete();
$web.Dispose();
# Revert Branding to SP Default
$site = Get-SPSite http://development/mysite
$site | Get-SPWeb -limit all | ForEach-Object { $_.MasterUrl = $_.ServerRelativeUrl + "/_catalogs/masterpage/v4.master";$_.Update() }
$site.Dispose()