Artifactory Pro upgrade - artifactory

Question

I've juste upgraded Artifactory Pro from 5.8.3 to 6.5.2 release. It does not start properly and outputs this error in log files:
2018-11-09 10:31:56,360 [art-init] [INFO ] (o.a.s.a.e.c.V600DecryptAllUsersCustomData:28) - Start decrypting all users custom data
2018-11-09 10:31:56,465 [art-init] [ERROR] (o.a.s.SecurityServiceImpl:2537) - Could not decrypt user props/keys, cause:
org.jfrog.access.client.AccessClientHttpException: HTTP response status 500:Failed on executing /api/v1/users/, with response: {
"errors" : [ {
"code" : "INTERNAL_SERVER_ERROR"
} ]
}
at org.jfrog.access.client.http.AccessHttpClient.createRestResponse(AccessHttpClient.java:161)
at org.jfrog.access.client.http.AccessHttpClient.restCall(AccessHttpClient.java:112)
at org.jfrog.access.client.AccessClientBaseImpl.findAll(AccessClientBaseImpl.java:77)
at org.jfrog.access.client.AccessClientBaseImpl.findAll(AccessClientBaseImpl.java:68)
at org.jfrog.access.client.user.UsersClientImpl.findUsers(UsersClientImpl.java:49)
at org.artifactory.security.SecurityServiceImpl.decryptAllUserProps(SecurityServiceImpl.java:2512)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at org.springframework.aop.support.AopUtils.invokeJoinpointUsingReflection(AopUtils.java:317)
at org.springframework.aop.framework.JdkDynamicAopProxy.invoke(JdkDynamicAopProxy.java:201)
at com.sun.proxy.$Proxy146.decryptAllUserProps(Unknown Source)
at org.artifactory.security.access.emigrate.conveter.V600DecryptAllUsersCustomData.convert(V600DecryptAllUsersCustomData.java:29)
at org.artifactory.environment.converter.local.version.MarkerFileConverter.convertIfExistsAndDeleteMarkerFile(MarkerFileConverter.java:46)
at org.artifactory.security.SecurityServiceImpl.convert(SecurityServiceImpl.java:312)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at org.springframework.aop.support.AopUtils.invokeJoinpointUsingReflection(AopUtils.java:317)
at org.springframework.aop.framework.JdkDynamicAopProxy.invoke(JdkDynamicAopProxy.java:201)
at com.sun.proxy.$Proxy146.convert(Unknown Source)
at org.artifactory.converter.ConvertersManagerImpl.serviceConvert(ConvertersManagerImpl.java:167)
at org.artifactory.spring.ArtifactoryApplicationContext.refresh(ArtifactoryApplicationContext.java:249)
at org.artifactory.spring.ArtifactoryApplicationContext.<init>(ArtifactoryApplicationContext.java:136)
at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62)
at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
at java.lang.reflect.Constructor.newInstance(Constructor.java:423)
at org.artifactory.webapp.servlet.ArtifactoryContextConfigListener.configure(ArtifactoryContextConfigListener.java:207)
at org.artifactory.webapp.servlet.ArtifactoryContextConfigListener.access$200(ArtifactoryContextConfigListener.java:63)
at org.artifactory.webapp.servlet.ArtifactoryContextConfigListener$1.run(ArtifactoryContextConfigListener.java:88)
2018-11-09 10:31:56,470 [art-init] [ERROR] (o.a.c.ConvertersManagerImpl:216) - Conversion failed. You should analyze the error and retry launching Artifactory. Error is: Could not decrypt user props/keys, see logs for more details
Does someone already had this kind of issue ? Thanks for clues.