Error as org.apache.fop.fo.UnknownXMLObj

Hello All,
In logs of our application, I am getting the following error:

No LayoutManager maker for class class org.apache.fop.fo.UnknownXMLObj

I tried googling in different angles but could not really get to a conclusion as to how I should go about investigating it.

Can someone give some inputs as what might cause this error?

Our application uses the following versions (I am not sure whether I should include any other information):

Fop 0.93.0.Patch3
Velocity/Apache 1.5.0
Velocity-Tools/Apache 1.4.0

Thanks in advance for your valuable inputs.

Thanks,
Debasmita