c# - Entity Framework save changes to context causing error -

i trying save changes context has 2 items. 1 new, other old. able list of objects , save single item no issues, moment have 2 items , call save bombs out saying:

store update, insert, or delete statement affected unexpected number of rows (0). entities may have been modified or deleted since entities loaded. refresh objectstatemanager entries.

snippet of code below.

thank you.

    protected bool save(params t[] entities)     {         foreach (t entity in entities)         {             bool b = context.entry<t>(entity).member<int>(string.format("{0}id", typeof(t).name)).currentvalue > 0;              if (b)             {                 context.context.attach(entity);                 context.entry<t>(entity).state = system.data.entitystate.modified;             }             else             {                 context.context.add(entity);                 context.entry<t>(entity).state = system.data.entitystate.added;             }         }         return context.savechanges() > 0;     } 

needed primary key on table auto generated.