This is in an application I am using called Mirth, but it appears to be coming from inside an Apache Commons library from a method that checks if something is indeed Base64
It's likely an ArrayIndexOutOfBoundsException. The -61
is supposedly the index.
From http://kickjava.com/src/org/apache/commons/codec/binary/Base64.java.htm:
134 private static boolean isBase64(byte octect) {
135 if (octect == PAD) {
136 return true;
137 } else if (base64Alphabet[octect] == -1) { // <---
138 return false;
139 } else {
140 return true;
141 }
142 }
Apparently the input isn't Base64 encoded.