Step 1) Check all GST account they Add GST % in the account they one of Reason not allowed to save new Product with Other GST %
Step 2)There is Item wise Sales/purchase Account and not select Account OF sales and Purchase account that why show Message select Sales and Purchase account at the time of save Product
Step 3) At the time of old product Modified not select HSN /SAC code also show Message Please select HSN/SAC code