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The base/system default Soft Key Template name/s have changed between version of CUCM
The workaround is to change the Soft Key Base template to one that exist in target.
Open Object Browser from Wrangler UCMC open Object Browser menu for the Soft Key template in question by selecting from menu Objects → Browse, then . Then from All Object Types drop down, select CUCM-SOFTKEY-TEMPLATE
Select the Soft Key Template in question to display detail, in . In the override value column drop down adjacent to Base Softkey Template, select a Base Soft Key Template that exist in Target, then Save Changes
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