导入对象是预期的Golang 1.4.2中的错误

I have just upgraded Golang from 1.3 to version 1.4.2. And cannot compile due to error:

../../my/mandrill.go:5: import /path/to/go/home/pkg/darwin_amd64/github.com/keighl/mandrill.a: object is [darwin amd64 go1.3.3 X:precisestack] expected [darwin amd64 go1.4.2 X:precisestack]
FAIL    folder [build failed]

on line m "github.com/keighl/mandrill"

package my

import (
    "fmt"
    m "github.com/keighl/mandrill"
)

I guess some rules of importing have changed in 1.4.2. But cannot figure out how to change my import code to make it compile.

Just delete the old pkg files, usually it upgrades automatically though.

rm -rf $GOPATH/pkg/

I met this problem too. I deleted the old packages but still get same error. finally I found the old pkg keep get generated by my "sublime text2". after restarted it. everything back to work :p