I have the version 18.104.22.1687 (build 267)of multiterm and I cant open the files .mtw and .mta, which I have been provided by my client.
You can't - .mtw files (plus the associated other files - two sets of .mdf, .mta and .mtf files) are used by MultiTerm 5.x, whereas you have MultiTerm iX.
I also tried to convert those files with Multiterm convert. It then gives me some error messages or/and ask me for some user id and password. I havent been provided with any. What shall I do?
What exactly are the error messages you're getting?
Which application is asking you for a user ID, and at which point?
Best regards, Ralf