| 1 | initial version |
First, i can not reproduce your problem on Sage 7.4.beta6. Which version are you using ? Perhaps upgrading will solve your issue.
Meanwhile, you should fix your problem by explicitely transforming your symbolic expression into a floating-point number:
sage: point([RDF(real_part(zeta(I))+1),0])
Launched png viewer for Graphics object consisting of 1 graph
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