did you try measures to improve convergence (see e.g.
http://www.intusoft.com/articles/converg.pdf)? You will find more info
if you google 'spice convergence'.
You may also have a look at chapt. 22.214.171.124 of the actual manual.
Please send the complete input file (including exciting voltages,
options and commands). Otherwise nobody might be able (and willing) to
have a look at the error.