Do you have some left over data which already has 3560 or whatever number is next to be used?
If you cannot access the database direclty, like in cloud environments, create an additional page over the entity so you can find the data.
could you also check the stack trace below-
ERROR - Connector: An error has occurred while handling the request. [User 'Abhijith' with session id '962f9fe5-a77d-456d-9ab9-45c67c9fc8da' and roles 'Admin'] 2015-03-23 10:32:02.028 ERROR - Connector: com.mendix.core.CoreRuntimeException: com.mendix.core.CoreRuntimeException: com.mendix.core.CoreRuntimeException: Exception occurred in action '{"type":"CreateAction","entityName":"DB.Generate"}', all database changes executed by this action were rolled back at hG.a(SourceFile:183) Caused by: com.mendix.core.CoreRuntimeException: com.mendix.core.CoreRuntimeException: Exception occurred in action '{"type":"CreateAction","entityName":"DB.Generate"}', all database changes executed by this action were rolled back at hG.b(SourceFile:217) Caused by: com.mendix.core.CoreRuntimeException: Exception occurred in action '{"type":"CreateAction","entityName":"DB.Generate"}', all database changes executed by this action were rolled back at com.mendix.core.actionmanagement.CoreAction.c(SourceFile:515) Caused by: com.mendix.core.CoreRuntimeException: Failed to retrieve autonumber value for object 'DB.Generate at im.a(SourceFile:917) Caused by: l: An exception has occurred for the following request(s): fr@1282169b at x.a(SourceFile:49) Caused by: l: Exception occurred while retrieving data. (SQL State: 42501, Error Code: 0) at H.a(SourceFile:1394) Caused by: org.postgresql.util.PSQLException: ERROR: permission denied for sequence db$generatematchidmxseq at org.postgresql.core.v3.QueryExecutorImpl.receiveErrorResponse(QueryExecutorImpl.java:2101) at org.postgresql.core.v3.QueryExecutorImpl.processResults(QueryExecutorImpl.java:1834) at org.postgresql.core.v3.QueryExecutorImpl.execute(QueryExecutorImpl.java:255) at org.postgresql.jdbc2.AbstractJdbc2Statement.execute(AbstractJdbc2Statement.java:510) at org.postgresql.jdbc2.AbstractJdbc2Statement.executeWithFlags(AbstractJdbc2Statement.java:386) at org.postgresql.jdbc2.AbstractJdbc2Statement.executeQuery(AbstractJdbc2Statement.java:271) at org.apache.commons.dbcp.DelegatingPreparedStatement.executeQuery(DelegatingPreparedStatement.java:96) at org.apache.commons.dbcp.DelegatingPreparedStatement.executeQuery(DelegatingPreparedStatement.java:96) at H.a(SourceFile:313) at H.a(SourceFile:209) at H.a(SourceFile:159) at H.a(SourceFile:148) at z.a(SourceFile:41) at dA.a(SourceFile:192) at dA.a(SourceFile:150) at dA.a(SourceFile:83) at dE.a(SourceFile:68) at x.a(SourceFile:43) at h.a(SourceFile:269) at im.a(SourceFile:906) at hi.a(SourceFile:65) at hi.c(SourceFile:28) at hi.executeAction(SourceFile:17) at com.mendix.systemwideinterfaces.core.UserAction.execute(SourceFile:57) at com.mendix.core.actionmanagement.CoreAction.call(SourceFile:457) at hG.b(SourceFile:206) at hG.a(SourceFile:174) at com.mendix.core.Core.instantiate(SourceFile:708) at gx.execute(SourceFile:31) at jf.a(SourceFile:321) at com.mendix.externalinterface.connector.RequestDispatching$Worker.a(SourceFile:170) at com.mendix.externalinterface.connector.RequestDispatching$Worker$a.a(SourceFile:161) at com.mendix.externalinterface.connector.RequestDispatching$Worker$a.apply(SourceFile:160) at akka.actor.Actor$class.apply(Actor.scala:545) at com.mendix.externalinterface.connector.RequestDispatching$Worker.apply(SourceFile:156) at akka.actor.LocalActorRef.invoke(ActorRef.scala:910) at akka.dispatch.MessageInvocation.invoke(MessageHandling.scala:25) at akka.dispatch.ExecutableMailbox$class.processMailbox(ExecutorBasedEventDrivenDispatcher.scala:223) at akka.dispatch.ExecutorBasedEventDrivenDispatcher$$anon$4.processMailbox(ExecutorBasedEventDrivenDispatcher.scala:123) at akka.dispatch.ExecutableMailbox$class.run(ExecutorBasedEventDrivenDispatcher.scala:195) at akka.dispatch.ExecutorBasedEventDrivenDispatcher$$anon$4.run(ExecutorBasedEventDrivenDispatcher.scala:123) at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145) at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615) at java.lang.Thread.run(Thread.java:744) at akka.dispatch.MonitorableThread.run(ThreadPoolBuilder.scala:192)