At a guess - and since we can't access your database that's all it can be - it's taking too long for some reason. You could try the advice here:
MySQL Bugs: #61807: Fatal error encountered during data read[
^] but if that doesn't solve it, you'll need to use the debugger to look at the whole exception object and see if there is any further info in the InnerException or stack trace.
We can't do that for you!