Hello chifang1,
first, my Extension Manager is situated here: Program Files (x86)/Adobe/Adobe Extension Manager CC/Adobe Extension Manager CC.exe. From there I start it. In my case the CC manager mamnages cc and so too the 2014 extensions.
Please explore the following sources. First of all I would have a look there: http://helpx.adobe.com/pdf/extension_manager_reference.pdf. At many places, so too here - it is noted this "Important note: MXP type extensions are not supported in Extension Manager CC. The MXP format has been replaced by the ZXP extension format. An MXP extension can be converted to a ZXP extension using the “Convert MXP Extension To ZXP” tool which can be found in the Tools menu in Extension Manager CS6." This might be a possible sources of error.
Then, did you try to download your ext-manager from there: http://www.adobe.com/exchange/em_download/ and could you explore esp. this bundle: http://helpx.adobe.com/extension-manager/topics/extensions.html?
To avoid these problems I work with the both, DWCC and DW 2014 simultaneously. Ok, that does not sound so good, but for me it is easier, than hold up with a complicated troubleshooting.
Hans-Günter