TestLink

I have testlink_1.8_rc3b. when I've been updating (I chose "Migration from 1.7.2 (or greater) to 1.8.0 ") there were errors:
1) THE MESSAGE :: SQL [2265] executed [took 0.0001 secs][all took 0.7719 secs]: UPDATE testprojects SET prefix='НГР(ID=1543)', tc_counter=0 WHERE id=1543 Query failed: errorcode[1062] errormsg:Duplicate entry 'НГ' for key 2
ERROR ON exec_query() - database.class.php
1062 - Duplicate entry 'НГ' for key 2 - UPDATE testprojects SET prefix='НГР(ID=207)', tc_counter=0 WHERE id=207
2) THE MESSAGE :: SQL [2269] executed [took 0.0001 secs][all took 0.7727 secs]: UPDATE testprojects SET prefix='НГР(ID=103)', tc_counter=0 WHERE id=103 Query failed: errorcode[1062] errormsg:Duplicate entry 'НГ' for key 2
ERROR ON exec_query() - database.class.php
1062 - Duplicate entry 'НГ' for key 2 - UPDATE testprojects SET prefix='НГР(ID=1065)', tc_counter=0 WHERE id=1065
When I chose "Requirement Specification document " after updating Requirement Specification was dublicated.

What must I do before installation to avoid this error?

migration is not required i suppose, you can copy the files of 1.8.0 to the installed flder of 1.8rc3 folder.

Thank It's help me .