ORA 1555 while export in 9.2.0.6.0

Hello,
While doing export of a big table (approximately 35 GB) in production ,
I'm getting error like
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ORA-01555: snapshot too old: rollback segment number 1 with name "_SYSSMU1$" too small
Export terminated successfully with warnings.
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Shall i ignore this error or  Workaround if any please?

Also whats the advantage ot using buffer while export?

Regards,
Dhananjay