Sorry for the late response, but this is the case:
I have an ‘old’ cryptap.us wallet and have all the (secret) information about this wallet. When I enter
https://jswallet.github.io/#[myprivatekeyfromthiswallet] I get a screen in a myriadcoin jswallet with a new myriadcoinadres and don’t know how to proceed. Can you please explain in steps what I have to do from there so I get control over the XMR-coins in my (old) wallet?
I see now. jswallet will *not* work with "[myprivatekeyfromthiswallet]", what you need is the the random brainwallet phrase from the previous link. The private key is derived from that phrase, and it's not possible to go backwards. If you have the private key, I would suggest Myriadcoin-core and "importprivkey" from the debug console.