Access not allowing users to delete rows

I've got a problem with being able to delete rows of data in a form (for example, if I need to delete a row that I just duplicated, I can't do it). Here's a little bit about my database. I have three different habitats (forest, wetland, grassland) and each habitat has its own data entry form for entering a list of the species encountered at each site. The only difference in the forms is the name, all code is the same as are the settings for the forms and the controls. The forms consist of a main form (ForestSpeciesMain) and a subform (开发者_开发技巧ForestSpeciesSubform).

My problem is that I can't delete rows of data in the forest form. I click on the far left box just outside the row to select it and then hit right click to delete, and the selection for "Delete Record" is grayed out. I can't delete simply by hitting delete, either.

I've run the "Documenter" to double check the settings for the main form and the sub form and in both instances "AllowDeletions" is true, so technically I could delete records, but I can't. Does anyone have any ideas for what could be causing the problem?

The recordsource for the subform is a table, dbo_ForestSpeciesListM (SQL Server tables, Access used for data entry) and I can't delete records directly from the table, either.