Duplicate key value error

I am getting the following error while saving my data:
Caused by: com.haulmont.cuba.core.global.RemoteException: ERROR: duplicate key value violates unique constraint "erp_delivery_order_pkey" Detail: Key (id)=(14fb948b-0302-2bcb-f176-2581fbfd7049) already exists. at com.haulmont.cuba.core.sys.ServiceInterceptor.aroundInvoke(ServiceInterceptor.java:129) ~[na:na] at sun.reflect.GeneratedMethodAccessor265.invoke(Unknown Source) ~[na:na] at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:1.8.0_151] at java.lang.reflect.Method.invoke(Method.java:498) ~[na:1.8.0_151] at org.springframework.aop.aspectj.AbstractAspectJAdvice.invokeAdviceMethodWithGivenArgs(AbstractAspectJAdvice.java:629) ~[spring-aop-4.3.14.RELEASE.jar:4.3.14.RELEASE] at org.springframework.aop.aspectj.AbstractAspectJAdvice.invokeAdviceMethod(AbstractAspectJAdvice.java:618) ~[spring-aop-4.3.14.RELEASE.jar:4.3.14.RELEASE] at org.springframework.aop.aspectj.AspectJAroundAdvice.invoke(AspectJAroundAdvice.java:70) ~[spring-aop-4.3.14.RELEASE.jar:4.3.14.RELEASE] at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:168) ~[spring-aop-4.3.14.RELEASE.jar:4.3.14.RELEASE] at org.springframework.aop.interceptor.ExposeInvocationInterceptor.invoke(ExposeInvocationInterceptor.java:92) ~[spring-aop-4.3.14.RELEASE.jar:4.3.14.RELEASE] at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:179) ~[spring-aop-4.3.14.RELEASE.jar:4.3.14.RELEASE] at org.springframework.aop.framework.JdkDynamicAopProxy.invoke(JdkDynamicAopProxy.java:213) ~[spring-aop-4.3.14.RELEASE.jar:4.3.14.RELEASE] at com.sun.proxy.$Proxy119.commit(Unknown Source) ~[na:na] at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:1.8.0_151] at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:1.8.0_151] at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:1.8.0_151] at

It seems that the primary key generated is duplicate!
what could be the issue?