Improve error message

Author: martin-steinegger

Diff for: src/prefiltering/ungappedprefilter.cpp

@@ -404,7 +404,8 @@ int prefilterInternal(int argc, const char **argv, const Command &command, int m
     if (par.gpu == true) {
         const bool isGpuDb = DBReader<unsigned int>::getExtendedDbtype(tdbr->getDbtype()) & Parameters::DBTYPE_EXTENDED_GPU;
         if (isGpuDb == false) {
-            Debug(Debug::ERROR) << "Database " << FileUtil::baseName(par.db2) << " is not a valid GPU database\n";
+            Debug(Debug::ERROR) << "Database " << FileUtil::baseName(par.db2) << " is not a valid GPU database\n" 
+              << "Please call: makepaddedseqdb " << FileUtil::baseName(par.db2) << " " << FileUtil::baseName(par.db2) "_pad\n";
             EXIT(EXIT_FAILURE);
         }
     }