database migration

Hi, when we are trying to migrate from ver. 2.6.7_05 to ver. 2.7.4_01 or 2.7.1 we are getting this error, do you have any insight on how to solve this. 

Caused by: com.objectdb.o.InternalException: Unexpected internal exception
at com.objectdb.o.CLS.T(CLS.java:389)
at com.objectdb.o.CLS.S(CLS.java:351)
at com.objectdb.o.CLS.R(CLS.java:328)
at com.objectdb.o.CLS.Q(CLS.java:289)
at com.objectdb.o.CST.Vo(CST.java:634)
at com.objectdb.o.QRR.g(QRR.java:247)
at com.objectdb.o.QRR.f(QRR.java:153)
at com.objectdb.jpa.JpaQuery.getSingleResult(JpaQuery.java:750)
at com.example.dao.AplikacijaDAO.isInitialized(AplikacijaDAO.java:36)
at com.example.clara1.Clara1UI.initVideoConference(Clara1UI.java:118)
at com.example.clara1.Clara1UI.init(Clara1UI.java:65)
at com.vaadin.ui.UI.doInit(UI.java:687)
at com.vaadin.server.communication.UIInitHandler.getBrowserDetailsUI(UIInitHandler.java:214)
at com.vaadin.server.communication.UIInitHandler.synchronizedHandleRequest(UIInitHandler.java:74)
at com.vaadin.server.SynchronizedRequestHandler.handleRequest(SynchronizedRequestHandler.java:41)
at com.vaadin.server.VaadinService.handleRequest(VaadinService.java:1414)
... 54 more
Caused by: com.objectdb.o.UserException: Failed to deserialize (com.objectdb.o.UserException; local class incompatible: stream classdesc serialVersionUID = 7838610279947510067, local class serialVersionUID = 4460369539292383939)
at com.objectdb.o.MSG.d(MSG.java:75)
at com.objectdb.o.BYR.Y(BYR.java:810)
at com.objectdb.o.BYR.Y(BYR.java:749)
at com.objectdb.o.CLS.T(CLS.java:383)
... 69 more
Caused by: java.io.InvalidClassException: com.objectdb.o.UserException; local class incompatible: stream classdesc serialVersionUID = 7838610279947510067, local class serialVersionUID = 4460369539292383939
at java.io.ObjectStreamClass.initNonProxy(ObjectStreamClass.java:616)
at java.io.ObjectInputStream.readNonProxyDesc(ObjectInputStream.java:1843)
at java.io.ObjectInputStream.readClassDesc(ObjectInputStream.java:1713)
at java.io.ObjectInputStream.readNonProxyDesc(ObjectInputStream.java:1843)
at java.io.ObjectInputStream.readClassDesc(ObjectInputStream.java:1713)
at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:2000)
at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1535)
at java.io.ObjectInputStream.readObject(ObjectInputStream.java:422)
at com.objectdb.o.BYR.Y(BYR.java:784)
... 71 more

It may indicate using different ObjectDB versions on the client and on the server.

could you please clarify your answer, old objectdb is on one server, new 2.7.. version is on another server, the log i attached is generated by wildfly 10.1 server. Both wildfly versions are the same. When we move db files from the old objectd 2.6.. to new objectdb 2.7.. server we are getting this error.

Are you using ObjectDB in client-server mode? If you do you should upgrade both sides together.