generate portable version cannot addon plugin(buffer var)

I installed gVim7.4 in win7_x64, and add on some plugins, it uses good. Now I want to change it to a portable version. I copied the Vim folder to another folder and name it gVim74, I uninstalled Vim. The common edit is good of the portable version, but the plugins not fully added.
There is a plugin(plugina.vim), it defined variable "b:plugina_var", when I run the plugin, can not find b:plugina_var. I have source the plugina.vim in _vimrc, and I already put it into vim74/plugin. I source plugina.vim manually again, it works OK.
So why the buffer variable b:plugina_var cannot define in portable version? Is there some environment variables that I need notice when produce a portable version of vim?

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