It's almost a sure thing that the computer with playback problems
doesn't have the font the presentation uses. When the needed font is
missing, PowerPoint (or Windows) substitutes another one.
Even though the fonts are the same point size, the letters in different
fonts can be considerably taller or shorter and may "set" much wider.
In other words, text that perfectly filled a box in the correct font
may overflow badly when a different font is substituted.
Open the presentation on the computer with the problem and choose
Format, Replace Fonts. Look at the list of fonts in the upper listbox
on the Replace Fonts dialog box. Any that have a "?" Icon next to them
are fonts that the presentation need, but that are missing on the
computer.
Either install the font on the computer or try embedding it in the PPT
when saving the PPT file from the computer where you've created the
presentation.