to relink the login to the correct id you will have to run (I assume that the login is appuser, and the databas user appuser):
alter user appuser with login = appuser ;
From BOL:
To change the name of a user requires ALTER ANY USER on the database. To change the default schema requires ALTER permission on the user. Users can change only their own default schema.
Requires CONTROL permission on the database to remap a user to a login
As you explained that you have the db_owner role on the database, it should work.
SQL Server Management Studio Startup
When Microsoft's SQL Server Management Studio (SSMS) starts it tries to connect the Certificate Revocation List (CRL) of Microsoft:
http://crl.microsoft.com/pki/crl/products/MicrosoftRootAuthority.crl
The underlying .NET components of SSMS are trying to contact the Certificate Revocation List and SSMS is unable to do so. This slows down the overall loading procedure. (15 seconds per certificate apparently)
Ok so here is what is happening. SSMS has a high percentage of managed code, all of this code is signed when we ship it. At start up (if this setting is checked) the .Net Runtime tries to contact crl.microsoft.com to ensure that the cert is valid(there were some fake certs issued in Microsoft’s name a while back so this is a very valid concern). If there is no internet connection or there is a problem contacting the certificate revocation list server then this will delay SSMS startup.
Reference: FAQ, Why does SSMS take 45s to start up? (MSDN Blog)
One issue that can cause this problem is that if the server does not have access to the internet, then the .NET framework can’t access the crl.microsoft.com website to verify that the digital signatures used to sign the binaries for managed applications are valid. Each certificate check has a 15 second timeout in the .NET runtime implementation. Depending on what features are installed, this can add up to a minute of startup time for Management Studio.
Reference: SQL Server Management Studio Startup Time (MSDN Blog)
Solutions
You can circumvent part of the issue, by downloading the certificate directly be entering the link into your browser and then importing the certificate to your certificate database
You can reconfigure your (company's) firewall to allow connections to Microsoft's CRL
You can reconfigure your personal antivirus/firewall to allow connections to the Microsoft CRL
You can configure your (company's) firewall to send a timeout faster to your client for requests accessing Microsoft's CRL.
You can configure IE to no longer "Check publisher's certificate revocation" in the advanced settings.
(See above mentioned blogs 1 and 2 for details)
Best Answer
Are you restoring to an existing instance of the DB? If so then space issues shouldn't be particularly relevant. At our place we run the following as job steps in restore jobs:
This will kill all system processes (spids) against your DB. As someone else mentioned ensure there is an agreement with users that this will occur, or that other system processes require it etc.
Hopefully these steps will add some resiliance.
NB: Assumes you run the DB in multi_user !