Model is unsuitably constrained (i.e. there were still some variables left to be computed, and some unusable equations left over).
At the time of the error, the following variables were found:
 * Undefined: ca_SR in component gating_rel
 * Defined: koCa in component gating_rel
 * Defined: kiCa in component gating_rel
 * Defined: ec50SR in component gating_rel
 * Defined: MaxSR in component gating_rel
 * Defined: MinSR in component gating_rel
 * Undefined: kCaSR in component gating_rel
 * Undefined: koSRCa in component gating_rel
 * Undefined: kiSRCa in component gating_rel
The following equations couldn't be used:
 * Equation with no id on the apply or math element.
 * Equation with no id on the apply or math element.
 * Equation with no id on the apply or math element.