hi ilona -
what kind of polaroid back are using ?
over the years my 545 back has failed a bunch of times.
the metal end gets jammed (like you talk about), the tab-springgy-thingy stopps latching onto the metal end &C too. my local repair guy was able to take it apart and fix it, wasn't expensive.
while it was in the shop, i got antsy and bought a
#500 back as a spare. it is olde, thin, and allegedly for obsolete film. (i was turned onto it by a friend). this junk-back bought for 15$ works better than the 545. the rollers spread the pod of chems more evenly, and it hasn't failed in 6 years of use (not to mention the use it got before me). the only thing that can go wrong is the tab-springgy-thingy is sometimes removed and there isn't a stop to prevent you from removing the whole sheet of paper when you are ready to expose. you just need to pull it " enough " ( kind of like the russian saying about making tea " how is your tea so good? ahh, you add just enough water"
hope you get yours working, but just in case i added a link to a cheep replacement
- john