By default the LTS is deployed to 15 hive in SharePoint 2013. In this case, you have to redeploy the solution in 14 hive as well.
First, run the following cmdlets on the machine hosting the NMSP service. (Run as administrator)
Add-PsSnapin Microsoft.SharePoint.Powershell
Install-SPSolution -Identity dell.nmsp.admin.wsp -GACDeployment -CompatibilityLevel {14,15} -AllWebApplications -confirm:$false –force
Install-SPSolution -Identity dell.nmsp.frontend.wsp -GACDeployment -CompatibilityLevel {14,15} -AllWebApplications -confirm:$false –force
iisreset
After these steps are performed, you can see the ‘Migrator for Notes to SharePoint settings’ item under Site Collection Administration catalog after clicking ‘Site Settings’ in SP2010 site.
The final step that must be performed is as follows, please search all ‘nmsp*.aspx’ files under 14 hive (for example, C:\Program Files\Common Files\microsoft shared\Web Server Extensions\14)
Search open each file and do a find/replace ‘MasterPageFile="seattle.master"’ with ‘MasterPageFile="~/_layouts/applicationv4.master"’.
This should allow the IS/LTS to work in 2010 mode now.