warning 1 light on

I have a 1 series BMW and last week it had the EGR valve replaced and the system all cleaned, it now has warning 1 light on which the book says can cause adverse damage to exhaust emissions, is it okay to drive, and what does it actually mean??

I need some help with this and do you think the garage will help with no charge as they carried the work out last week?

Thanks in advance :-)