Actually this issue is still repeating in mid 2013. As stack trace is obfuscated looks like:
at xe86f37adaccef1c3.xc5c3f438428cb03b.x446c2c253cdada74(x561fa53c007d3597 xe01ae93d9fe5a880)
at xe86f37adaccef1c3.xc5c3f438428cb03b.xb7e46440d2a34d6d(x561fa53c007d3597 xe01ae93d9fe5a880, FieldMergingArgs& xfbf34718e704c6bc)
at xfbd1009a0cbb9842.x561fa53c007d3597.x67bf65e8693cdf2e(xc5c3f438428cb03b xa4d52e34b62b5495)
at xfbd1009a0cbb9842.x561fa53c007d3597.x83bcdf1790545fdb()
at Aspose.Words.Fields.Field.x42a25ae95099edb8(x5e36356bc92c609b x0f7b23d1c393aed9)
at Aspose.Words.Fields.Field.x295cb4a1df7a5add(x5e36356bc92c609b x0f7b23d1c393aed9)
at xfbd1009a0cbb9842.xfedf115fd9c03862.x4e3cfc222c92cda7(Field xe01ae93d9fe5a880, x5e36356bc92c609b x0f7b23d1c393aed9)
at xfbd1009a0cbb9842.xfedf115fd9c03862.x4e3cfc222c92cda7(Field xe01ae93d9fe5a880)
at xfbd1009a0cbb9842.xbf9ddf72e1283af9.x18dfca7c5fd2402f()
at xfbd1009a0cbb9842.xfedf115fd9c03862.xdd6cf0348a23f220(xcf417e2db4fe9ed3 xe00c282e1a49fcfb)
at xfbd1009a0cbb9842.xfedf115fd9c03862.xdf269951086089ce(x6435b7bbb0879a04 xa942970cc8a85fd4)
at xe86f37adaccef1c3.xc5c3f438428cb03b.xd01ea9131ba53b87(ArrayList x292b5f49fee42032, xfedf115fd9c03862 xcc5022025f73a533)
at xe86f37adaccef1c3.xc5c3f438428cb03b.xdeeb682062ef79a5()
at xe86f37adaccef1c3.xc5c3f438428cb03b.xd5da23b762ce52a2(xa11a4c48b53f49a6 xef1769c4fe6ae4ca, Boolean xc9c7b90943167aed)
at Aspose.Words.Reporting.MailMerge.x18dfca7c5fd2402f(xa11a4c48b53f49a6 xef1769c4fe6ae4ca)
at Aspose.Words.Reporting.MailMerge.Execute(String[] fieldNames, Object[] values)