There is often no need for a new checkout or copying.
I have just solved a similar issue relating to the error “previous operation has not finished” with help from this (Link)
It seems that svn sometimes gets stuck while processing commands/operations.
All of these operations are stored in the database file wc.db in the .svn folder.
By downloading SQLite to my checkout directory and running
sqlite3.exe .svn/wc.db "select * from work_queue"
you can get a list of all pending operations. These operations are the ones the error is referring to as “not finished”.
By running
sqlite3.exe .svn/wc.db "delete from work_queue"
all of the old operations are deleted from the work queue and the error disapears.
No need for a new checkout or anything