References using Mendeley MS Word Plugin do not exist if the word file is opened in another machince

Hi, I love using Mendeley for managing bibliography. I use Mendeley MS Word plugin for adding references automatically in MS Word documents. When I add any references in MS word document using the plugin in my laptop (Windows Vista, MS Word 2003), it perfectly works. I also use Dropbox cloud to use those documents in my office PC (Windows XP Professional MS Word 2003). Again, I can add references in MS word by using the Mendeley Plugin at my office PC. However, when I open my existing MS word files, which were edited at my laptop, all links are gone though all existing references are there!!! Same thing happens when I open any file (created @my office PC) from my laptop, the links are gone!! Is there any solutions? Many thanks