When running a schema compare with an offline snapshot taken of the whole server, I get the "Exception of type 'System.OutOfMemoryException' was thrown" error.
You cannot compare a single database/schema to a snapshot of the whole server.
To use Schema Compare, take a snapshot of a single database/schema to compare with. This can be done through the snapshot option from within Schema Compare. Only use the server snapshot when running a server compare.
Please refer to SOL45767 about a problem accessing Create Snapshot feature before running a schema compare.