The size of all gaps in all models is limited to the same default value. Most systems, including CATIA version four, Computervision's CADDS, and Spatial Technology's ACIS (employed by AutoCAD, Ashlar Vellum, IronCAD, SolidDesigner, and TurboCAD), employ a fixed tolerance model. Unfortunately, no other major CAD firms have adopted this strategy. The relative tolerance model is a clever one, and it enables Pro/E to run fast. So for large models, such as jet engines, Pro/E allows larger gaps, while for small models, such as watch parts, only small gaps are permitted.
The maximum gap is a fraction of the total model size. Pro/Engineer employs a variable tolerance model. Unfortunately, different systems employ different strategies for computing this tolerance. In such cases, the user might receive a message that the model is "corrupted." Consequently, all systems employ a strategy for computing the maximum allowable gap, or "tolerance zone," between an edge and the two faces it bounds. The system can no longer distinguish the inside of a part from the universe around it. If the gaps between edges and faces become too large, solid-modeling programs can become confused about the boundaries of the model. Here is some information from an article I got from the web What MCAD package is the data native to? It could be that the data contains a lot of surfaces or complex geometry.
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