An empty cell is displayed as @ in a crosstab in IBM Cognos Insight, instead of no value being shown. IBM TM1 Architect shows all the values correctly.
An invalid format was set in element attributes for the dimension. In this case a c:"" was set, to exchange all 0 values with an empty space only for this one dimension.
Resolving the problem
Set a format as described in the documentation: http://pic.dhe.ibm.com/infocenter/ctm1/v10r1m0/topic/com.ibm.swg.ba.cognos.tm1_ug.10.1.0.doc/c_tm1displayformats_n70007.html#TM1DisplayFormats_N70007
Example pattern: #,##0.00;(#,##0.00);"";"" .
The first two values in this pattern, represent the positive and negative values. The 3rd and the 4th value represent zero and NULL values. This will format all values with two decimals and zero or NULL values will be displayed as empty string.