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Try assigning the new roles to the listitem object and not to the file object. 
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Whenever I add an Item with Item level permission to a List/Library, that user is added with Limited Access permission to that List/Library. May be beacuse of this, when the document is opened for editing hangs the system. 

<pre><code class="code-10 nolinks" id="code-264656">if (!spfile.Item.HasUniqueRoleAssignments)
 spfile.Item.BreakRoleInheritance(true);
web.AllowUnsafeUpdates = true;
 
#region REMOVE ALL USER'S PERMISSIONS
SPRoleAssignmentCollection spRoles = spfile.Item.RoleAssignments;
for (int j = spRoles.Count - 1; j &gt; -1; j--)
spRoles.Remove(j);
#endregion
 
SPRoleDefinition RoleDefinition = web.RoleDefinitions.GetByType(SPRoleType.Contributor);
SPRoleAssignment RoleAssignment = new SPRoleAssignment(UserID, &quot;email&quot;, &quot;name&quot;, &quot;notes&quot;);
RoleAssignment.RoleDefinitionBindings.Add(RoleDefinition);
web.AllowUnsafeUpdates = true;
spfile.Item.RoleAssignments.Add(RoleAssignment);
</code></pre>
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Whenever I add an Item with Item level permission to a List/Library, that user is added with Limited Access permission to that List/Library. May be beacuse of this, when the document is opened for editing hangs the system. 

Sharepoint Item Level Permissions

Microsoft Sharepoint is a software platform and family of software products used for collaboration and web publishing combined. These capabilities include developing web sites, portals, intranets, content management systems, search engines, wikis, blogs, and other tools for business intelligence and collaboration. SharePoint has a Microsoft Office-like interface, and it is closely integrated with the Office suite.