2963411 - Import of legacy custom theme into portal fails - File build error.

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A theme transported from one NW Java Portal (source) to another NW Java Portal (target) via zip cannot be imported due to the following error:

#2.0�#<YYYY MM DD HH:mm:ss:ms>#+0200#Error#com.sap.portal.theming.migration.PortalLessMigrationService#
#EP-PIN-TOL#sap.com/com.sap.portal.theming.portalthemespersistence#C0000AE6225303A600000002000076D3#8230252000000004#sap.com/com.sap.portal.themes.archive#com.sap.portal.theming.migration.PortalLessMigrationService#<USER>#6##FFB962E2DBD711EAC8BE0000007D956C#2abdc66ddc5511eac50d0000007d956c##0#Thread[HTTP Worker [@919566749],5,Dedicated_Application_Thread]#Plain##
Failed to convert theme <THEME_NAME> from old structure to new structure
[EXCEPTION]
java.lang.RuntimeException: org.mozilla.javascript.JavaScriptException: sap.theming.less.CompilationException:File build error.
   in code "sap.theming.less.File.build"
   while processing entity <ENTRY>
CAUSED BY <CAUSE>
   called by "[object Object]" of type "sap.theming.less.LessCompiler"
   in code "sap.theming.less.LessCompiler.sFileToCss"
   in file <FILE_NAME>
   in line <LINE> column <COLUMN>
   Extract:
      Line <LINE-1>:<LINE-1_CONTENT>;
      Line <LINE>:<LINE_CONTENT>;
      Line <LINE+1>:<LINE+1escape(unit(@_CONTENT>;
CAUSED BY <CAUSE>
   at com.sap.ui.theming.engine.scripting.ScriptEngine.executeJS(ScriptEngine.java:163)
   at com.sap.ui.theming.engine.scripting.ScriptEngine.executeJSWithEngineClassLoader(ScriptEngine.java:187)
   at com.sap.ui.theming.engine.service.ServiceBase.evalJavaScriptWithEngineClassLoader(ServiceBase.java:159)
   at com.sap.ui.theming.engine.service.ServiceBase.evalJavaScriptFileRelative(ServiceBase.java:239)

• NetWeaver Application Server Java
• Enterprise Portal

sap.theming.less.LessCompilationException:error evaluating function `unit`: the first argument to unit must be a number called by "[object Object]" of type "sap.theming.less.LessCompiler theme designer editor portal migration transport , KBA , CA-UI2-THD , Theme Designer , EP-PIN-TOL , Themes / Portal UI Theme Designer / Theme Editor , Problem