I'm getting this LinkageError with 4.2.2GA with default settings on Debian Linux. When you install JBoss via apt-get on Debian Linux, this is the default version. It doesn't happen on a 4.0.2 installation, which I have access to on a Sun server. Here's a simple JSP to reproduce the problem. <% try { javax.crypto.Mac mac = javax.crypto.Mac.getInstance("HmacSHA1"); if (mac == null) { out.print("No Mac found for HmacSHA1"); } else { java.security.Provider provider = mac.getProvider(); out.print("Mac instance: "+mac.getClass().getName()+"\r\n"); out.print("Provider: "+provider.getClass().getName()+" - "+provider.getInfo()+"\r\n"); out.print("Algorithm: "+mac.getAlgorithm()+"\r\n"); } } catch (Exception e) { out.print("Exception thrown, while inspecting crypto for HmacSHA1\n"+e.getMessage()+"\r\n"); } catch (LinkageError le) { out.print("Linkage error in javax.crypto.Mac\r\n"+le.getMessage()+"\r\n"); } %> View the original post : http://www.jboss.com/index.html?module=bb&op=viewtopic&p=4170717#... Reply to the post : http://www.jboss.com/index.html?module=bb&op=posting&mode=reply&a...