Having trouble cutting 3 sec off of file

[thinders]

Using 2.7

On w10

File is mpg

Copy Mode

I set the A and B markers on the 3 sec to remove from the beginning of the file.

I use the up  down arrow keys to ensure that the B marker is on an I frame.

After setting B maker,  Save with output set to Mpeg-PS ff

I get the following errors as seen in Attachments 1 - 3

Thanks .....

[thinders]

SUE= Stupid User Error.....file was mp4 not mpg ........ working as expected....