First, you should check both the syntax and the .acm file you use as input. Either one may be incorrect. Start from the simplest explanation first. If there is no fault in either your syntax or your input file, then perhaps more complex solution are in order.

Thanks dear Imam Salehudin for the comprehensive explanation. I checked carefully the syntax, didn't find anything wrong. As for the .acm file, I produced it simply run the output option. Seems it's on format. Please tell me how to check the .acm file.

You can check the .acm file using the output file generated when you process the raw data in PRELIS. It is possible that an error occur during processing. Check on the number of variable, since it is mentioned in the error message.

You may also want to compare the number of variables in the raw data and in the .acm output.

Thanks. I'll do that again, although I'm pretty sure that I did check it before. I'll let you know the result shortly.

Hey Hotniar, Did you ever solve this problem? I'm having the same problem right now. My data is a mix of ordinal and continuous. I've tried everything I can think of to run it but everytime no matter what data I use I still get this message.

Dear Samantha,

I tried the suggestion provided by Imam Salehudin, but unfortunately it didn't work out. I checked the .acm file...it seems nothing wrong. I'm pretty sure there's no wrong with the syntax as I generated the .acm file simply by clicking generate the .acm file. I'll get back again to data analysis when I have enough time. I'll let you know any progress.

Thanks for your response Hotniar! It's so frustrating - I haven't made any progress on my situation either. I've tried running it in MPlus instead and although I haven't fixed it, I'm thinking this might be a better software because more people have experience with it. I'll let you know if I discover anything about our error message. Best of luck to you!

Thanks Samantha. Best of luck to you as well.

Dear Hotniar,

You may refer to the following link:

http://davidakenny.net/cm/respec.htm

Dear Mahfuz,

Many thanks. The link is very helpful. I will allocate time to read the link throughly.

Dear Hotniar and Mahfouz,

I see that you wrote for almost two year ago, but maybe a simple and potentially helpful response might help others running into the same problem, searching for a solution, so I offer a suggestion. This problem sometimes occur due to pointing to the ACM file in the syntax, while the acm file happens to be located not in the same directory. As you are using the system file, you don't need to point to the acm file in your syntax. There will be a pointer in the system file to the acm anyway if you specify an acm file using the Output Options in PRELIS. Run the syntax without anything like Asymptotic Matrix from file blabla.acm. 

This will lead to using Robust maximum likelihood as the method of estimation. 

Hope this helps! 

Ata Ghaderi