I logged in to system using Firebird.SQL.Client and everythin was OK, but suddenly I got this exception:
 Stack trace:
[IscException: database
No message for error code 335544528 found]
FirebirdSql.Data.Client.Native.FesServiceManager.ProcessSatatusVector(IntPtr[] statusVector) +105
FirebirdSql.Data.Client.Native.FesServiceManager.Attach(...) +184
FirebirdSql.Data.Client.Native.FesServiceManager.Open() +253

[FbException (0x140000d0): database
No message for error code 335544528 found]
FirebirdSql.Data.Services.FbService.Open() +602
FirebirdSql.Data.Services.FbService.QueryService(..)
FirebirdSql.Data.Services.FbService.ProcessQuery(..)
FirebirdSql.Data.Services.FbService.Query(..)
FirebirdSql.Data.Services.FbServerProperties.GetInfo(..)
FirebirdSql.Data.Services.FbServerProperties.GetString(...)
EntityFramework.Firebird.FbProviderServices.GetDbProviderManifestToken()

[InvalidOperationException: Could not retrive storage version.]
EntityFramework.Firebird.FbProviderServices.GetProviderManifestToken(DbConnection connection)
System.Data.Entity.Core.Common.DbProviderServices.GetProviderManifestToken(DbConnection connection)

[ProviderIncompatibleException: The provider did not return a Provider ManifestToken string]
...

[ProviderIncompatibleException: An error occured accessing the database. This usually mean that the connection to database failed. Check that the connection string is correct..]

This stack trace was retyped from image so can have any errors. Original image with stack trace attached

I did not see such issues on 6.6.0.0