Internal Server Error when deleting a sub-task

2013-10-18 12:36:46,073 com.atlassian.mywork.client.reliability.DefaultUnreliableWorker:thread-4 WARN Matt_Shelton 749x738x1 1rcdgrt 10.56.24.100 /rest/subtasks-create/1.0/facility/issue/CAPD-1847 [mywork.client.reliability.DefaultReliabilityService] Failed task "{"username":"Matt_Shelton","type":"POST","json":"{\"globalId\":\"appId=4152ef42-1783-351e-b10a-415b5489000d&entity=issue&id=15500\",\"condition\":{},\"metadata\":{\"watching\":true}}","path":"/rest/mywork/1/notification/metadata"}"
com.atlassian.sal.api.net.ResponseException: 500 - Internal Server Error
        at com.atlassian.mywork.client.reliability.DefaultUnreliableWorker$2.handle(DefaultUnreliableWorker.java:136)
        at com.atlassian.mywork.client.reliability.DefaultUnreliableWorker$2.handle(DefaultUnreliableWorker.java:120)
        at com.atlassian.applinks.core.auth.trusted.TrustedApplinksResponseHandler.handleNormally(TrustedApplinksResponseHandler.java:46)
        at com.atlassian.applinks.core.auth.trusted.TrustedApplinksResponseHandler.handle(TrustedApplinksResponseHandler.java:34)
        at com.atlassian.applinks.core.auth.ApplicationLinkRequestAdaptor$1.handle(ApplicationLinkRequestAdaptor.java:87)
        at com.atlassian.plugins.rest.module.jersey.JerseyRequest$2.handle(JerseyRequest.java:166)
        at com.atlassian.sal.core.net.HttpClientRequest.executeAndReturn(HttpClientRequest.java:336)
        at com.atlassian.plugins.rest.module.jersey.JerseyRequest.executeAndReturn(JerseyRequest.java:161)
        at com.atlassian.applinks.core.auth.ApplicationLinkRequestAdaptor.execute(ApplicationLinkRequestAdaptor.java:84)
        at com.atlassian.applinks.core.auth.trusted.TrustedRequest.execute(TrustedRequest.java:39)
        at com.atlassian.mywork.client.reliability.DefaultUnreliableWorker.send(DefaultUnreliableWorker.java:119)
        at com.atlassian.mywork.client.reliability.DefaultUnreliableWorker.access$200(DefaultUnreliableWorker.java:26)
        at com.atlassian.mywork.client.reliability.DefaultUnreliableWorker$1$1.run(DefaultUnreliableWorker.java:77)
        at com.atlassian.sal.core.executor.ThreadLocalDelegateRunnable.run(ThreadLocalDelegateRunnable.java:38)
        at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
        at java.lang.Thread.run(Unknown Source)
Exception in thread "com.atlassian.mywork.client.reliability.DefaultUnreliableWorker:thread-4" java.lang.RuntimeException: com.atlassian.sal.api.net.ResponseException: 500 - Internal Server Error
        at com.atlassian.mywork.client.reliability.DefaultUnreliableWorker$1$1.run(DefaultUnreliableWorker.java:92)
        at com.atlassian.sal.core.executor.ThreadLocalDelegateRunnable.run(ThreadLocalDelegateRunnable.java:38)
        at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
        at java.lang.Thread.run(Unknown Source)
Caused by: com.atlassian.sal.api.net.ResponseException: 500 - Internal Server Error
        at com.atlassian.mywork.client.reliability.DefaultUnreliableWorker$2.handle(DefaultUnreliableWorker.java:136)
        at com.atlassian.mywork.client.reliability.DefaultUnreliableWorker$2.handle(DefaultUnreliableWorker.java:120)
        at com.atlassian.applinks.core.auth.trusted.TrustedApplinksResponseHandler.handleNormally(TrustedApplinksResponseHandler.java:46)
        at com.atlassian.applinks.core.auth.trusted.TrustedApplinksResponseHandler.handle(TrustedApplinksResponseHandler.java:34)
        at com.atlassian.applinks.core.auth.ApplicationLinkRequestAdaptor$1.handle(ApplicationLinkRequestAdaptor.java:87)
        at com.atlassian.plugins.rest.module.jersey.JerseyRequest$2.handle(JerseyRequest.java:166)
        at com.atlassian.sal.core.net.HttpClientRequest.executeAndReturn(HttpClientRequest.java:336)
        at com.atlassian.plugins.rest.module.jersey.JerseyRequest.executeAndReturn(JerseyRequest.java:161)
        at com.atlassian.applinks.core.auth.ApplicationLinkRequestAdaptor.execute(ApplicationLinkRequestAdaptor.java:84)
        at com.atlassian.applinks.core.auth.trusted.TrustedRequest.execute(TrustedRequest.java:39)
        at com.atlassian.mywork.client.reliability.DefaultUnreliableWorker.send(DefaultUnreliableWorker.java:119)
        at com.atlassian.mywork.client.reliability.DefaultUnreliableWorker.access$200(DefaultUnreliableWorker.java:26)
        at com.atlassian.mywork.client.reliability.DefaultUnreliableWorker$1$1.run(DefaultUnreliableWorker.java:77)
        ... 4 more