Can not restore a dumped database

[Josef Springer <Josef.Springer@xxxxxxxxx>]

iI habe dumped a database with
pg_dump --file="<filename>" -a  --schema="OfficeTalk" -h localhost
-U OfficeTalk  "OfficeTalk"

Restoring it with 
pg_restore -d "OfficeTalk" -a -h localhost -U "OfficeTalk" "<filename>"

i get the error 
pg_restore: [archiver] input file does not appear to be a valid archive

What to do ?

                   mit freundlichen Grüßen / best regards,
               Josef Springer
               (Geschäftsleitung/Management)

	Address	Josef.Springer@xxxxxxxxx	Orlando-di-Lasso Str. 2	D-85640 Putzbrunn
	Office	+49 (0)89 600 6920
	Fax	+49 (0)89 600 69220
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-- the software company --