Revert downgrading of log error->warn->error

use const error message POSSIBLY_CORRUPTED_HISTORY, add more guidance

src/historywork/CheckSingleLedgerHeaderWork.cpp

@@ -7,6 +7,7 @@
 #include "history/HistoryArchive.h"
 #include "history/HistoryManager.h"
 #include "historywork/GetAndUnzipRemoteFileWork.h"
+#include "main/ErrorMessages.h"
 #include "util/GlobalChecks.h"
 #include "util/Logging.h"
 #include "util/TmpDir.h"
@@ -84,9 +85,16 @@ CheckSingleLedgerHeaderWork::doWork()
     }
     else if (mGetLedgerFileWork->getState() != State::WORK_SUCCESS)
     {
-        CLOG_WARNING(History,
-                     "Failed to download ledger checkpoint {} from archive {}",
-                     mFt->baseName_gz(), mArchive->getName());
+        CLOG_ERROR(
+            History,
+            "Failed to download ledger checkpoint {} from archive {}: {}",
+            mFt->baseName_gz(), mArchive->getName(),
+            POSSIBLY_CORRUPTED_HISTORY);
+        CLOG_ERROR(
+            History,
+            "If this occurs often, consider notifying the archive "
+            "owner. As long as your configuration has any valid history "
+            "archives, this error does NOT mean your node is unhealthy.");
         return mGetLedgerFileWork->getState();
     }
 

src/main/ErrorMessages.h

@@ -11,7 +11,7 @@ constexpr auto const REPORT_INTERNAL_BUG =
     "Please report this bug along with this log file if this was not expected";
 constexpr auto const POSSIBLY_CORRUPTED_HISTORY =
     "One or more of history archives may be corrupted. Update HISTORY "
-    "configuration entry to only contain valid ones";
+    "configuration entry to only contain valid ones.";
 constexpr auto const POSSIBLY_CORRUPTED_LOCAL_FS =
     "There may be a problem with the local filesystem. Ensure that there is "
     "enough space to perform that operation and that disc is behaving "