ORA-39126 and ORA-01017 while executing dbms_datapump import over database link

I hit this problem when executing DBMS_DATAPUMP IMPORT operation over database link. Here is the full error message:

Starting "SYS"."import_MYTASK":
ORA-39126: Worker unexpected fatal error in KUPW$WORKER.POST_MT_INIT [SELECT SYS.KUPM$MCP.GET_ENDIANNESS@MYDBLINK FROM SYS.DUAL]
ORA-04052: error occurred when looking up remote object SYS.KUPM$MCP@MYDBLINK
ORA-00604: error occurred at recursive SQL level 3
ORA-01017: invalid username/password; logon denied
ORA-02063: preceding line from MYDBLINK
ORA-06512: at "SYS.DBMS_SYS_ERROR", line 95
ORA-06512: at "SYS.KUPW$WORKER", line 8164
----- PL/SQL Call Stack -----
object line object
handle number name
70000058f38e5b8 19028 package body SYS.KUPW$WORKER
70000058f38e5b8 8191 package body SYS.KUPW$WORKER
70000058f38e5b8 2072 package body SYS.KUPW$WORKER
70000058f38e5b8 1438 package body SYS.KUPW$WORKER
70000058e31ea78 2 anonymous block
Job "SYS"."import_MYTASK" stopped due to fatal error at 09:33:35

Database link was working fine when i query manually. Restarting database solved the problem however i dont know what was the cause...