Reading SV assertion values using FSDB reader library

[newuser11]

I am trying to read an assertion signal from a fsdb file using fsdbReader library.

As given in the Fsdb Reader document, I used

ffrObject::ffrAddToSignalList( fsdbVarIdCode)

and

ffrObject::ffrLoadSignals to load the varId

But it throws error

/************************************
*WARN* Failed to load the FSDB file.
The FSDB file should be regenerated.
If the error still exists, contact your local Synopsys support for help.

*WARN* Internal error of the currently executed program. Please restart the program.
. If the error still exists, contact your local Synopsys support for help.
******************************************/

I understand there could be different set of APIs to read assertion values changes.
But it's not very clear from the fsdbReader document.

If you know the APIs, please share them.

Thanks,