If you are not using a shift function and you read in multiple sets of relaxation data for different temperatures, you should get a different set of prony coefficients for each temperature. If you include a shift function as part of the curve fitting, you need to specify what the master curve is.
I suggested just trying to curve fit one temperature because that is often easier to trouble shoot when the curve fitting is not working out.
The images below show a successful curve fit with 20C using the data you provided. I used 7 terms and seeded the relaxation times to go from 1 sec to 1e7 because that sometimes helps produce a better fit. It doesn't matter if the relaxation times for each term are not in ascending order. Just think of it as seven terms in a mathematical prony expression to represent the relaxation of the modulus over time. Also, I think there might be more then one solution to this problem. In other words, using different numbers of terms and using default seed values might produce another combination of prony terms that is equally valid for matching the relaxation behavior.
I hope this helps.
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