I get the following error after I upgraded Jenkins as well as the plugin:

16:51:33 FATAL: com.mks.connect.UserApplicationSessionImpl$SSLSocketFactory.createSocket(Ljava/lang/String;ILjava/net/InetAddress;ILorg/apache/commons/httpclient/params/HttpConnectionParams;)Ljava/net/Socket;
16:51:33 java.lang.AbstractMethodError: com.mks.connect.UserApplicationSessionImpl$SSLSocketFactory.createSocket(Ljava/lang/String;ILjava/net/InetAddress;ILorg/apache/commons/httpclient/params/HttpConnectionParams;)Ljava/net/Socket;
16:51:33 at org.apache.commons.httpclient.HttpConnection.open(HttpConnection.java:707)
16:51:33 at org.apache.commons.httpclient.MultiThreadedHttpConnectionManager$HttpConnectionAdapter.open(MultiThreadedHttpConnectionManager.java:1361)
16:51:33 at org.apache.commons.httpclient.HttpMethodDirector.executeWithRetry(HttpMethodDirector.java:387)
16:51:33 at org.apache.commons.httpclient.HttpMethodDirector.executeMethod(HttpMethodDirector.java:171)
16:51:33 at org.apache.commons.httpclient.HttpClient.executeMethod(HttpClient.java:397)
16:51:33 at org.apache.commons.httpclient.HttpClient.executeMethod(HttpClient.java:323)
16:51:33 at com.mks.connect.UserApplicationSessionImpl.handleHTTPResponse(UserApplicationSessionImpl.java:304)
16:51:33 at com.mks.connect.UserApplicationSessionImpl.getSession(UserApplicationSessionImpl.java:350)
16:51:33 at com.mks.connect.UserApplicationSessionImpl.getSessionURI(UserApplicationSessionImpl.java:413)
16:51:33 at com.mks.connect.HttpCmdRunnerImpl.getSessionURI(HttpCmdRunnerImpl.java:72)
16:51:33 at com.mks.connect.HttpBlimpInputStream.getSessionURI(HttpBlimpInputStream.java:125)
16:51:33 at com.mks.connect.HttpBlimpInputStream.blimpInitiate(HttpBlimpInputStream.java:152)
16:51:33 at com.mks.connect.BlimpInputStream.getInputStream(BlimpInputStream.java:223)
16:51:33 at com.mks.connect.BlimpInputStream.readNoEof(BlimpInputStream.java:693)
16:51:33 at com.mks.connect.BlimpInputStream.handleNextBlimpCommand(BlimpInputStream.java:266)
16:51:33 at com.mks.connect.BlimpInputStream.read(BlimpInputStream.java:190)

When I downgrade to Jenkins 1.419 everything works fine again!