Hello, Mariko.
The Genome Graphs tool does not use BED format, but rather uses its own format.  From http://genome.ucsc.edu/cgi-bin/hgGenome, when you click the “upload” button, please carefully read the “Upload file formats” section just below the “Paste URLs or data” text box.
If you cannot supply your data in Genome Graphs format, you could create a custom track from your BED file in our Table Browser (http://genome.ucsc.edu/cgi-bin/hgTables; see also http://genome.ucsc.edu/goldenPath/help/hgTablesHelp.html) and then use the “import” button in Genome Graphs to import your custom track.  Note that this will transform the track into Genome Graphs format with a certain window size and it might look different depending on the scale of view.
Please contact us again at gen...@soe.ucsc.edu if you have any further questions.  All messages sent to that address are archived on a publicly-accessible Google Groups forum.  If your question includes sensitive data, you may send it instead to genom...@soe.ucsc.edu.
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Steve Heitner
UCSC Genome Bioinformatics Group
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