SVGText is not rendered in jasperreport but works on Ireport

We use svgText to render image via Batik in Ireport like this (in an image expression)

net.sf.jasperreports.renderers.BatikRenderer.getInstanceFromText($F{svg_path})

In Ireport, it works but via our server (Jasperreport 5.2 / RJB 1.4 / Rails 3.2 / Ruby 1.9.3 ), we've got an error

net.sf.jasperreports.engine.fill.JRExpressionEvalException: Error
evaluating expression : Source text :
net.sf.jasperreports.renderers.BatikRenderer.getInstanceFromText($F{svg_path})

we have all Batik jar in our classpath in each case.

Someone has an idea ?