diff --git a/src/rssm.cpp b/src/rssm.cpp
index 17ff36d8d90d98de5f30f9d822e3e3c00e14f017..a35ac17e63cc7e70b70d07d0f05f5ef5863b8b00 100644
--- a/src/rssm.cpp
+++ b/src/rssm.cpp
@@ -68,7 +68,7 @@ void RssmRawFile::RdRawYam( FILE *F_in )
     y.checkvalue( "format" );
     val = y.getscalar( "format" );
     if( strncmp( val.c_str(), "acq5.1 for yaml1", 16 ) )
-        throw( string("Unexpected format") + val );
+        throw( string("Unexpected format: ") + val + " instead of acq5.1" );
     y.skipvalues( 2 );
     y.checktype( YAML_MAPPING_END_EVENT, "Meta: no end of map\n" );
 
@@ -633,7 +633,7 @@ void NRSSM::ReadSeries( int format, int flag )
                 break;
             }
         } else if( format==5 ) {
-            string fnam = fser+"u"+strg(isub);
+            string fnam = fser+"a"+strg(isub);
             FILE *F_in;
             if( !(F_in = fopen( fnam.c_str(), "r" ) ) )
                 break;