I have a couple of more questions:
1. Did you have a background proteome file? You can specify a Background Proteome at:
Settings > Peptide Settings > Digestion
and Skyline might use that in order to populate the Protein Description column in the Paste Peptides dialog
(although I would not expect this to be able to cause a hang like this).
2. In your screenshot, it looks like you were including extract stuff in the peptide sequence which would make Skyline reject it in the Paste Peptides dialog.
That is, one of your sequences for example looked like:
The "K." at the beginning and ".N" at the end are used elsewhere in Skyline to indicate the preceding and following amino acids in the protein sequence that the peptide came from. However, if you include that in the Paste Peptides dialog, Skyline will give you an error.