I have installed Mojo Portal on several other Arvixe hosted accounts and I just tried it on two new ones (and I have bought Joe much beer! - Thanks Joe!!).

I can no longer install Mojo Portal CMS with one click . The version now is 2.3.8.5.

In both cases I set the ASP.NET extension to 4.0 integrated first.

When it I attempt the Mojo Portal install it seems to be failing at the database create if the error message is accurate:
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The application could not be installed:
- Error while install application pack.
- Error while installing application package: The database 'master' could not be created.
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In both cases I gave valid names for the SQL Server databases to be created, but it seems to not pick up that name value and tries to create master instead. I got around this but will leave the ticket open with Arvixe to get them to repair the install routine.

At the site instance you will see this message:

Welcome to mojoPortal Setup
Probing system...
File system permissions ok.
The system cannot connect to the MSSQL database. Please check your connection string.
System.Data.SqlClient.SqlException (0x80131904): Login failed for user 'xxxx'. at System.Data.ProviderBase.DbConnectionPool.GetConnection(DbConnection owningObject) at System.Data.ProviderBase.DbConnectionFactory.GetConnection(DbConnection owningConnection) at System.Data.ProviderBase.DbConnectionClosed.OpenConnection(DbConnection outerConnection, DbConnectionFactory connectionFactory) at System.Data.SqlClient.SqlConnection.Open() at mojoPortal.Data.DBPortal.DatabaseHelperGetConnectionError(String overrideConnectionInfo)

Note: This page shows some information that is helpful during setup and upgrades but for security it would be best not to show any information when the system is up to date. You can disable setup and suppress all information on this page by setting DisableSetup=true in Web.config. When you need to upgrade, you can set this back to false. If you are logged in as Administrator setup will run and you will be able to see this page even if it is disabled in Web.config so you can easily leave it disabled and just login before upgrading. But if you are not logged in you will need to enable setup in Web.config.

Here's how I got around it:

After your first install attempt and you get the database error, go into the Arvixe control panel and create your own database and username with the same specifics you gave at the round one install attempt. Then go in and install Mojo again and specify exiting website and choose the db and user you created manually and let the install run again. The Mojo installers will then be able  to connect and create all your database objects the way it used to do so seamlessly before. 

I think this is an Arvixe issue and will stay after them, but it's pretty easy to get around this little hickup till they do. 

Q1 2012 the Mojo install was one click easy on Arvixe. Q2 2012, you have to play with it a bit to get it to work but it's still pretty painless.