[AMOS] Model is unidentified when control variable added

Amos - missing values for follow up survey

I'm using AMOS to analyse my data set which is comprised of a main survey and a follow up survey which was completed by about 70% of respondents. This means I have a lot of missing data for my follow up survey. Responses from the main survey should predict the response on the follow up survey.

I'm struggling to decide which is the best method for dealing with this problem, could anyone give me advice?

I couldn't find a way to change the thread title, sorry.
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