Are you able to access the SQL Server instance using SQL Server Management Studio?
Frederik
I got something similiar a year ago. I had to give up and install the site on another machine and then move to the web and sql server manually. The connection to the database worked just fine although not when trying to install a new site.
If SQL server instance is reachable from other sources then try to increase connection timeout in SQL server itself (in Management Studio):
Server -> Properties -> Connections -> Remote Query timeout.
The timeout limit is already set at 600 seconds and it times out in a shorter span than that, perhaps 30-60 seconds.
Can you execute aspnet_regsql.exe manually against that database?
aspnet_regsql -A all -S {server-name} -E -d {database-name}
I've seen this in the Migration Tool from CMS 4 to 5 when the database server name is an IP address - change the name to a 'proper' server name and it works...
It seems I can't create EpiServer sites anymore.
Whenever I do I get the following error, http://imgur.com/9R6wml0
Seems like the SQL server times out and I have no idea why.
Any help debugging this is much appreciated!