Backoffice login throwing class not found exception while logging

[Former Member]

while logging to backoffice version 6.7 with credential admin/nimda it is throwing below error.

 Apr 17, 2019 5:35:00 PM org.apache.catalina.core.StandardWrapperValve invoke
 SEVERE: Servlet.service() for servlet [zkLoader] in context with path [/backoffice] threw exception [Servlet execution threw an exception] with root cause
 java.lang.ClassNotFoundException: de.hybris.platform.solrfacetsearch.config.IndexConfig
         at org.apache.catalina.loader.WebappClassLoaderBase.loadClass(WebappClassLoaderBase.java:1892)
         at org.apache.catalina.loader.WebappClassLoaderBase.loadClass(WebappClassLoaderBase.java:1735)
         at ma.glasnost.orika.generated.Orika_FacetSearchConfig_FacetSearchConfig_Mapper193231375992907$4.mapAtoB(Orika_FacetSearchConfig_FacetSearchConfig_Mapper193231375992907$4.java)
         at ma.glasnost.orika.impl.mapping.strategy.UseCustomMapperStrategy.map(UseCustomMapperStrategy.java:77)
         at ma.glasnost.orika.impl.MapperFacadeImpl.map(MapperFacadeImpl.java:671)
         at ma.glasnost.orika.impl.MapperFacadeImpl.map(MapperFacadeImpl.java:650)
         at ma.glasnost.orika.impl.ConfigurableMapper.map(ConfigurableMapper.java:158)
         at de.hybris.platform.solrfacetsearch.config.impl.DefaultFacetSearchConfigService.getConfiguration(DefaultFacetSearchConfigService.java:51)
         at de.hybris.platform.commercesearch.searchandizing.boost.impl.DefaultBoostFacade.getFacetSearchConfig(DefaultBoostFacade.java:219)
         at de.hybris.platform.commercesearch.searchandizing.boost.impl.DefaultBoostFacade.getBoostRules(DefaultBoostFacade.java:64)
         at de.hybris.commercesearchbackoffice.widgets.boostviewer.controller.BoostViewerController$1.execute(BoostViewerController.java:112)
         at de.hybris.platform.commerceservices.impersonation.impl.DefaultImpersonationService$1.execute(DefaultImpersonationService.java:79)

[Former Member]

Check the solr index configuration.