Without much more detail, my instinct is that you may be missing the type of entity shown at the top of Form 510 or Form 511 under the PTE address section.
If you are filing a partnership return, please review page 2, Schedule B and confirm a selection has been made on box 1a, 1b, 1c or 1d. If you are filing an s corporation return, the s-corporation box would be automatically selected for you.
I hope this resolves the issue you are experiencing. If not, please provide some more detail. Thanks.