Look at this knowledgebase: "How do I give a computer user without administrator rights the proper file privilege to run Multisim?"
It is made for version 9 but it should apply for your version 7 as well. Although, I would recommend giving Full Control privileges to 'everyone' on all the EWB installation folder.
1. Click Start-->Run
2. Type "regedt32"
3. Locate HKEY_Classes_Root/Multisim.Document
4. On the menu, select Security-->Permission (win 2000), For XP select Edit-->Permission
5. Give full control for everyone
6. Repeat step 3-->5 for: