I've heard that this might be a bug in the installer in 5.2. There is some configuration where the repository app.config may be using one connection string to the database while an individual model is using a different one. It is required by SQL that snapshot isolation not use DTC and thus multiple connections with different strings causes this error.
It is a requirement that the configuration for repository web application in web.config match the models that are installed. This should be validated at run time but it appears our installer does not validate this... I suspect this occurs when model manager web is installed with different sql credentials then model manager data.
Check the Repository.Website\web.config for the setting below...
<repository server="localhost" database="vCAC" store="security.xml" />
Make sure the server, database and authentication setting match that in the table below...
SELECT *
FROM [DynamicOps.RepositoryModel].[Models]
Data Source=localhost;Initial Catalog=vCAC;Integrated Security=True;MultipleActiveResultSets=True
If they don't match, probably easiest to manually modify both to use windows authentication and restart iis and check if the issue persists. If this resolves the issue and you wish a different configuration, fool around with the settings some more and validate that this still works.