Bicycle Mechanics - chain skips only on small cog

I was having trouble shifting to the smallest rear cog (while on the large front chainring) b/c one of the jockey wheels would rub against the dropout.

It would shift to the smallest cog if I were on the smaller front chainring, so the LBS suggested lengthening the chain to reduce tension. It worked, and I can now shift to the smallest rear cog.

but I have a new problem. when I am on the smallest rear cog (and on the large front chain ring, i.e. in top gear), the chain skips. It does not skip on the other cogs.

my guess is that this means the chain is too long? I added only one link, so unfortunately I guess this means I either live with the skipping chain or temporarily having to go to the smaller front chainring in order to shift to the smallest rear cog.

bike is a Xootr Swift folder with Capreo hub and 9-speed cassette + 105 derailleur.

thanks for any tips.

jeez Capreo is only a 9t .. Chain replacement is step 1.
the wear of chain would really soon
transfer wear onto the 4~5 teeth that pulls the hub around ..

Sorry, I forgot to mention it is a brqnd new chain.

Have to be where the bike is to say anything else.. this forum is just text.

If it isn't related to chain or sprocket wear, and I'm assuming it isn't, I suspect that the trim is a bit off. Chain length is not a factor since the lower loop tension is set by the RD cage spring, and doesn't make a difference.

I suspect it's more of a trim issue - check lower limit screw - or possibly the hanger is a bit off plane. You might also use the "B" screw to optimize the pulley/sprocket distance.

Jockey pulley was hitting the dropout. Chain is lengthened. Still skips with new chain. There may still be interference with the dropout and pulley, not enough to keep it out of the gear, but enough to cause skipping. If more B screw tension doesn't help I'd try a spacer to get that dropout away from the gear.