This also happens to my sling patients from time to time. I have found that this problem is often associated with a non-relaxing urethral sphincter and/or pelvic floor muscle. In order to urinate, you have to relax the urethral sphincter, and lower your pelvic floor. Sometimes after surgery, some women have difficulty doing this, especially after pelvic floor surgery. Releasing or removing the sling usually does not help, especially if the sling is loose to begin with. Options for treatment include pelvic floor physical therapy to help loosen the pelvic floor muscles, flomax (a drug which can relax the urethral sphincter, - usually used on men who can't pee due to enlarged prostates - caution this can also lower blood pressure), and Botox injected into the urethral and pelvic floor muscles. The fact that you are having bladder spasms is a good sign, it means that your bladder muscle ( the Detrusor) is in good working order. Have your urogyn check your urethral pressure profile, and note the maximum urethral closure pressure. If both of these are in the normal range, then the sling is probably not too tight, and you may benefit from therapy to relax your pelvic floor muscles and urethral sphincter.