ERROR: COPY quote must be a single ASCII character

Dear all,

I have to copy the file with the following delimiters into the database:

||5354235||,||some text...||
||1234567||,||some text...||
||1234568||,||some text...||

The sql statement I defined was:

COPY testtable FROM 'test.txt' WITH DELIMITER AS ',' CSV QUOTE AS '||';

but the error:

ERROR: COPY quote must be a single ASCII character

Any solution? Thank you in advance.

Best, Andrej