--- a/road_cmd.c	Wed Apr 26 21:44:22 2006 +0000
+++ b/road_cmd.c	Wed Apr 26 21:48:22 2006 +0000
@@ -474,6 +474,7 @@
 		ret = DoCommand(tile, bits, 0, flags, CMD_BUILD_ROAD);
 		if (CmdFailed(ret)) {
 			if (_error_message != STR_1007_ALREADY_BUILT) return CMD_ERROR;
+			_error_message = INVALID_STRING_ID;
 		} else {
 			cost += ret;
 		}