One cause of an error on startup of RB is because it is trying to open a corrupt file.

If you get it open, close the project without saving by opening a different seq file. (Again, do not save the possibly corrupt file)
Close RB and see if it opens OK, then you'll know the file was the problem

After that you can try opening the backups of the file using 'File-Open backup' to see if it is OK, or you can whittle away at finding the error in the file.

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