query returns failed to read from database file

we have since today exceptions on executing some queries like this:

Failed to read from file 'F:\Hummingbird\Objectdb\db\coreSystemDb.odb'

we are using objectdb 2.7.2_05

in the objectdb log there is no message

it seams that this is only happening directly after startup (creating the database connection, factory ...).

our startup immediately activies the webSocket server ( after creating the database connection, factory ...), hundreds of requests (including the queries) are then received (what have been queued in the clients during down time)

Please post the full stack trace from the ObjectDB log file.