There are a lot of problems with this Fred Astaire-Ginger Rogers collaboration (Astaire as a ballet dancer being one of them), but it makes up for it all with a single, exquisite, extended bit of comedy between supporting players Edward Everett Horton and Eric Blore. Regulars in Astaire-Rogers pictures, they both specialized in ditheringly uptight double-takers, and a phone conversation they share here — in which they get lost in a morass of misspellings and misunderstandings — is their crowning achievement. I suppose the movie also has a few now-iconic George and Ira Gershwin numbers to its credit, including “Let’s Call the Whole Thing Off” and “They Can’t Take That Away from Me.” But the dancing that accompanies the music is sparse and sometimes uninspiring, including an awkward number in which Astaire and Rogers are saddled with roller skates. The convoluted plot, meanwhile, has something to do with marriage rumors about a respected ballet impresario (Astaire) and a famous nightclub performer (Rogers). Astaire doesn’t seem to know what to do with his character, while Rogers is miscast as a high-society snob. Add a subplot with a mannequin made to look like Rogers and a major production number in which 20 or so backup dancers wear eerie masks modeled on her face, and Shall We Dance is less likely to give you sweet dreams than nightmares.