This is occurring because the membership level has been defined to limit the number of cards at that level, to resolve the issue, change the number of cards allowed for the membership:
  1. Go to Memberships > Go into the specific Membership Program
  2. Go to the Membership Levels tab
  3. Highlight specific level
  4. Click Edit
  5. Adjust the number of cards allowed field
OR if this is the appropriate number of cards, but the member is downgrading to a lower level with less cards, use these steps: 
  1. Go to Constituents > Constituent search.
  2. Search for and select the constituent.
  3. Go to the Memberships tab.
  4. Click on the name of the membership program.
  5. Under the Member Cards section, highlight one of the cards and click Delete.
  6. If Delete is not able to be selected, click Clear Print Status, then click Delete.